Let's say the app you built costs X.
How much would you make the customer pay for the non-mantained source code as it is at that specific point?

I'm asking because I just found a library which costs 50$ for compiled version and 2000$ for source code

@molaram ok, but what would you base the price on?

@ZioCain depends, libraries are hard to price, easier for things like apps with subscriptions where you can ask how much could the owner of the source code make across 5-10 years? For libs, it's all about simple supply and demand / what will the market tolerate paying ?

How much would they have to pay you if they wanted you to maintain it? That might be a good starting point.

How much do they benefit from the deal? That defines the upper limit of what they will pay.

Perhaps they ask so much for the source code because they don't want anyone to see how bad it is :p