I don't have a huge amount of time now, but if I'm free later I'll try and add more. The general answer is: pretty expensive. Personal firearms, meaning firearms that could be held and fired by a single person, existed in the Fifteenth Century but were not widely used. Gunpowder weapon was still primarily in the form of artillery, usually used in sieges rather than battles. T.F. Tout wrote an article at the turn of the Twentieth Century that is still an excellent breakdown of the cost of firearms in England in the fourteenth to early fifteenth centuries. England in particular has great records for this kind of information. The Valois Dukes of Burgundy were the most famous advocates of gunpowder artillery in the late Fifteenth Century and while their records are excellent they have not been fully published anywhere and so are difficult to access.

I don't have exact figures in front of me, unfortunately, but I do remember that Tout explained that early guns were roughly priced by the pound, so the bigger the gun the more expensive it was. Guns on their own, though, were not too expensive, at least when compared to other examples of warfare equipment. Meaning they would be well out of the price range of a common peasant but probably affordable for a mid-level noble (an Earl/Count for example). What was prohibitively expensive was gunpowder, Saltpeter in particular. Saltpeter was insanely expensive at the start of the Fourteenth Century but went down in cost over the Fifteenth as Europeans developed effective methods of making it. Still, it was never cheap and gunpowder weapons used an awful lot of it. A local noble might be able to afford a firearm but he would likely not be able to afford the gunpowder to shoot it very often, as an example.

There's a lot of great material out there on medieval gunpowder at the moment. Kelly DeVries has made some great contributions in particular but he's hardly alone.

Interesting question with varying answers depending on your angle; what do you mean by value? Are you talking about monetary value or cultural value?(I think I might have misunderstood the question you asked, but I'll take a go at it regardless, since you said "I'm more looking for a general idea of value, rather than exact numbers")

I'll try to answer of the cultural value of firearms, and I'll try to answer this from the point of view of an average Anatolian (Ottoman) citizen, as firearms are ingrained into the very consciousness of the people living there; as demonstrated by a very popular folk saying; "At, Avrat, Silah" , translating to "Horse, Woman, Gun". I'll also go bit over your specified timeline, from 1443 to mid 1500s. I've picked 1443 as it saw the start of the crusade of Varna and the aftermath of the conflict saw the start of usage of firearms in the Ottoman military.

The cultural value of firearms within the region stems from two things, which are tied together, the male identity and bandits, and bandits can be viewed as a personification of the male identity. In terms of male identity, firearms directly relate to the concept of honor, power, dominance and untouchability (Elvan Ozalp).

Used at least since 1421 with the Düzmece Mustafa rebellion, firearms would become a part of the Janissary entourage by the late 1400s (although from what I have read they seemed to prefer bows as bows were move accurate than the arquebus), with pistols being integrated much later.

As for banditry and guns;

Firearms in the Ottoman empire were readily available to two groups, the military or the Eşkıya, the bandits. Coincidentally, the rise of banditry has its roots within the military of the Ottoman empire as it would often integrate vagrants, young villagers who left their village for various reasons, into the military, swelling the numbers of the musket bearing "sekban" who would turn to banditry after the end of hostilities. Banditry is nothing new to the region, but, according to Halil Inalcik in his "Military and fiscal transformation of the Ottoman Empire", saw a huge increase with the armament of peasant levied soldiers with firearms. Also, as stated, much later, by Koci Bey, a pamphleteer for the State, a peasant levied into the army would never return to his village, as he would value his gun and horse too much, and since the peasant is not worthy of military status, he would turn to banditry.

Firearms were not that uncommon in the countryside; Beginning with the rebellion of Prince Beyazid, firearms would become quite common in the countryside, peasants could acquire firearms cheaply from artisans manufacturing a surplus. Beyazid would go on to persuade many of these to his cause (to become Sultan), which would become a common practice (hiring vagrant peasants and letting them acquire firearms). An interesting document from the late 1500s paints this phenomenon quite nicely; a sanjacbeyi from Aydin was able to confiscate 1500 firearms from the peasants in his district (Ilgurel, Atesli Silahlarin Yayilisi).

It is also very important to look at Turkish literature, folk legends, and folk music and its portrayal of guns and bandits, which, in the eyes of the commoner would increase the social value, and glorify, both firearms and bandits. Such a folk tale would be the Epic of Koroghlu and for an example in music, "Hekimoğlu".

tl;dr Firearms had high social value and were relatively cheap in the Ottoman Empire, making them a relatively cheap investment for wanna be vagabonds

Sources;

Bandits and Bureaucrats: The Ottoman Route to State Centralization, by Karen Barkey

Halil Inalcik, "Military and fiscal transformation of the Ottoman Empire" (Halil Inalcik has quite afew wirintgs about firearms in the Ottoman Empire)

Mücteba İlgürel, “Osmanlı İmparatorluğunda Ateşli Silahların Yayılışı”

Elvan Özalp and Hande Karakiliç, "Gun Ownership in Turkey: The Legal Dimension and Mental Health Practices"

P.S. This is the longest answer I've given in Reddit, I am not sure if this answer would be considered off topic, or does not obey this sub-reddits rules, if so, I'll delete it

P.P.S. You said European, I sure hope you consider Ottoman Empire to be European...

Kind of an add-on question: Given the accuracy and ease of use of the early gunpowder weapons used by Europeans, how many people actually owned them for individual use? I can understand the value of mass-firing in formation on a military scale, but it seems like it would be hard to use one for hunting or something like that given how cumbersome and slow early guns seemed to have been.