I am an avid watcher of medievalist content on YouTube but have done little scholarly research of my own (I doubt my university login for most journal databases is still valid anyway). A common topic that comes up regarding warfare just prior to and during the Medieval period is the debate over what armour was typical of each century/decade, its associated cost in money, skill or natural resource, and its practicality (ergo whether lack of wealth led to the use of wholly useless armour). An off shoot of this is the gambeson vs leather jerkin problem in Hollywood and the assumption that poorer warriors went around in plain clothes and Medieval biker style jackets.
I would love to hear some insight from a specialist in this area on three main issues here:
How expensive was it for a common feudal subject or general infantry soldier to get a gambeson or other padded armour? (In relation to their means)
Was mail really so expensive that it was reserved for elites? (Again, cost relative to other commodities)
Did people save cost by going into battle in silly leather vests or were they generally sensible, choosing armour appropriate to the weapons they would be facing (gambeson to protect against slow arrows, cuts and lighter bludgeons)?
Also, if you think my question is flawed, go right ahead and tell me what a better question would be...just want to learn.
The time period you have selected is vast, and infantru armour changes enormously during this time. As best as we can find, most soldiers in the 8th century would have no body armour at all, but hopefully an early Medievalist like u/alriclofgar can address this in more detail.
I deal with the armour of common soldiers in the later Middle ages here. It is particularly important to remember that while armour was generally not provided by a king (though for large campaigns they seem to have bought armour to supplement their troop's equipment) many soldiers serving in late medieval battles (at least in England) were involved in some patronage relationship with a social superior; they may have their armour provided by a patron or an employer that they had a contract with. Finally, those serving in medieval armies were often drawn from the weather parts of the common people - either as a militia or (more likely in all but defensive wars) as a contracted, semi-professional soldiers.
In any case, while (hardened) leather armour was used as a supplement for mail armour in the 13th and earlier 14th century and while it was used protection in sport combats much later, I see little evidence it was a 'poor man's armour' in general - they seem to have preferred cloth.
Bow, you asked about the price of cloth armour, and ai can't find it. I've been looking for years! I can say that a brigandine at 17 shillings was a bit more than a month's wages for an English Archer. But I can't find a price for jacks.