You are going the right way... also check
http://eab.abime.net/ ..
Ebay is ok, but the best deals will be from other amiga owners on the forums. Amigakit, while providing excellent service is the most expensive route (and you will still need a power supply and software).
I did just order some 3.1 roms from Amigakit... the price was good. But I believe because of the nature of the computer itself (hard to find in good condition) Amigakit needs to double the price to make it worth the time and money of obtaining those machines, testing, restoring and possibly repairing them. So of course they are more expensive... but they also are guaranteed to be working.
Just keep asking and someone will undoubtedly cough one up.
Don't pay more than $200USD for one stock in GOOD condition.
Anything more than that is too much unless it comes with a lot of goodies (like an accelerator and monitor).
