Putting an actual monetary value, especially in relative modern terms, is always tricky for the medieval period. While the medieval economy in England was extensively monetised, even for low denomination transactions, there was an element of communalism and barter economy, especially in the Early Medieval period, that also can muddy the water somewhat.

Interestingly, for Early Medieval England, or at least the 10th Century, we actually do have an idea of how much specific animals are worth, even if we can't necessarily put a discrete price on the actual meat. Æthelstan's London legal code (Æthelstan VI Iudica Civitatis Lundoniæ) sets the value of an ox at a mancus (30d), a cow at 20d, a pig at 10d and a sheep at a Mercian shilling (4d, whereas a Saxon shilling was 12d). The tricky part with this information is then assessing these legally-set prices in terms of affordability. In the 1086 Domesday Book, the taxable value of a "hide" or "ploughland" of land (a productive unit rather than a discrete geographic measurement but very roughly averaged at about 120 acres) is very, very, very roughly approximated to a pound, or 240d. For a typical villein or villager tenant farmer holding a virgate of land, very roughly some 30 acres, his holding could therefore be roughly estimated to be worth around 60d. So, based purely on that estimate, a villein would be able to purchase 2 oxen or 3 cows a year.

This valuation, however, is extremely problematic. Domesday Book is extremely unclear as to how, precisely, the values for each settlement are calculated and recorded, and as a result, there is much debate over how much we can actually value land. It's never clear if, for, example, the value assigned to a settlement includes the various manorial appurtenances appended to it, its mill(s), meadows, pastures, forests, orchards etc., or applies solely to the worked arable land. Do the values shown actually apply only to those ploughlands worked by the 'lord's plough-teams' as service rent, or do they apply to all worked arable lands? It's not made clear whether, for example, a stated value of pound accounts for just the value of the rent paid by the tenants, the total gross income of the estate, or the net profit of the land once the subsistance needs of the peasantry and the estate have been taken into account. The current consensus tends towards the first estimate (Roffe, Decoding Domesday, 2007), if only because to estimate otherwise would place the burden of taxation so incredibly high that contemporary chroniclers would be sure to remark upon it and the unrest it caused, as they did regarding things like the Forestry Laws. Indeed, the total tax estimates from Domesday are considerably less than the post-Conquest tax levied by Cnut in 1016, which suggests that the tax burden indeed wasn't "all surplus goods." What this means, therefore, is that your average villein is likely to have had far more in his pocket for the year than just 60d.

Of course, it's hard to place a concrete value on arable income. The farmer and his household must, of course, feed themselves and render food, service or cash rent to their manor. It's possible that a farmer might specialise purely in arable crops, or purely in livestock, and might then simply exchange some of his produce with his neighbours in order to fill both of their pantries. A miller might charge multure for the use of the mill, which would provide him with a ready source of flour, but he might then sell surplus to afford other foods, or might indeed grow his own. Some individuals within a community might specialise: an oxherd or shepherd might be paid for their services in food render, or with money. A farmer who kept sheep would do so predominantly for the sale of the wool (which would be spun by his wife and daughters, if he had any), but would likely be able to slaughter older animals within the herd each year for mutton. The seventh century laws of Ine of Wessex state:

If a husband has a child by his wife and the husband dies,the mother shall have her child and rear it, and [every year] 6 shillings shall be given for its maintenance—a cow in summer and an ox in winter

This communal benefit likely doesn't necessarily represent an actual ox as much as it does a stake in a communal plough team, but it does suggest that even the more marginal in society - widows and orphans - were promised some availability of meat.

What typically makes meat scarce is the fact that it has to be stretched out to feed whole households over a great period of time. Animals were typically slaughtered each year on Martinmas, the 11th of November, accompanied by a great feast. The only exceptions would be the breeding stock necessary for the next year's herds, and the sheep who would be spending the winter busily growing their valuable fleece. The meat butchered at Martinmas therefore would have to suffice through the winter and the following spring, until the breeding stock had done their business and new animals were available. Typically this would mean that meat would have to be salted, smoked, dried, pickled or otherwise cured and preserved, and carefully rationed.

While pop-history likes to say that 'meat was for the lords, the peasantry couldn't afford it', this should perhaps more accurately state that fresh meat was more of a luxury, especially in any great quantity. One of the reasons for this post-1066 was the Forestry Laws which considerably limited the rights of the peasantry to hunt. Game animals could provide a regular source of fresh meat - venison, boar, pheasant, grouse etc. - to the tables of the elite across the seasons, which was closed to the peasantry. Prior to 1066, hunting had also been popular among the peasantry: a hunter of deer and boar, and a birdcatcher and falconer are 'regular' community figures who appear within the 10th Century Ælfric's Colloquy. That's not to say that the peasantry stopped hunting after 1066, of course, they just had to be far more circumspect about it. This meat is even harder to value, since, technically, it's free, and as an illicit good post-1066, it's unlikely to have been sold openly at market.

One source of cheap, regular meat for the peasantry in any season was fish. The fisherman in Ælfric's Colloquy doesn't place a numerical value on his catch, but does have this to say:

I get into my boat, put my nets into the river and then I cast my bait and wicker baskets, and whatever I catch I take... I throw out the unclean ones and I take the clean ones for food for myself. [I sell my catch to] The townsfolk. I cannot catch as many as I can sell... I catch eels, pike, minnows and dace, trout, lamprey and any other species that swim in the rivers, like sprats.

A coastal fisherman might catch:

herring, salmon, dolphins, sturgeon, oysters, crabs, mussels, cockles, flatfish, plaice, lobsters and such like.

One interesting source for the rough pricing of foodstuffs is the 15th century poem London Lickpenny, a source I go to regularly. The poem follows a poor Kentish farmer (the titular 'lickpenny' or lack-penny) through the markets of London. Among the street foods available in the East Cheap markets are hot sheep's feet, beef ribs, a variety of meat pies, and whole mackerel. The titular character doesn't partake, having only a penny in his pocket with which he intends to pay the Billingsgate ferryman but instead buys a pint of wine, but their presence implies an affordability of these meat products to the general population on a regular basis.