I think the license is simple.

FMOD Shareware / Hobbyist License: you are a lone wolf, selling for just a few bucks, ie 10$ and you are not registred and it has to have "shareware" quality (proofed on a case by case basis). You pay once 100$. Honestly, most people don't exceed this type of license.

FMOD Casual License: intended for electronically distributed budget titles - titles must sell for $20 USD or less and be available through downloadable/online distribution channels only. Costs ~1500 $.

FMOD Commercial License: everything above that is commercial.

As long as you publish your game for free, you don't have to pay anything.

Chances are high, that most Indies don't sell their games for 10$ or more and then 100$ are very comfortable. If you make much money, 1500$ will peanuts, too. Don't get me wrong: I just think that if you really need it and you make real money with it, why complaining about such a low price for such a high quality middleware?

More information here: http://www.fmod.org/index.php/sales

Maybe you can tell us more details about your game and I can tell you what you have probably to pay..

Best regards,
-Chistian