I think some of you have already sold some pictures for different occasions, so maybe someone could help me with the following problem:

How much money could an amateur like me could take if someone want to use his pictures. Up to know I sold two times some pictures. The first time it was someone who need some pictures as decoration for a restaurant. He offered me 200$ for four pictures. The next time I got 200  Pounds for 10 images  from an tourist agency.  They always  wanted  them  as digital data, not as a print.

I was quite happy about this, but of course I don't know if it was a reasonable prize. At the moment I have two other offers. One is a picture for a book title. No idea how much they should pay me.

There's also someone  who wants to use them on his webpage and offered me a prize like on pages as istockphot.com. It's something like 3$ for a midsize picture. That's not really much money.

At the moment I always ask the people how much they want to pay, but of course, that could be stupid, if they offer a less money as it would be reasonable.

Are there any webpages or other sources to get information about prizes for pictures. Or has someone of you experiences with that and could give me some hints?