Make sure you make a contract for the current deal. And spell out very clearly that you own the rights to the code. In fact document the ownership of any and every aspect you can think of.

A lot of costs won't go down. The payent processing fees go down if you find another service provider and/or manage to negotiate a better deal (probably not possible if he's with one of the three places I recently mentioned). Hosting and bandwidth costs are not likely to fall either. Certainly dealing with support issues and paying other people won't be falling in costs either.

Just remember too, that since it was his idea, he could have gone to anyone to write the initial code. I gather it's all becoming a bit of a commodity as I understand your explanation, but if you do place value on his distribution powers, it sounds to me like you're coming out of this ok.

You may also find there's room for a greater stake later on by expanding the software again or perhaps working together on other projects. As long as both of you know if advance what you want (and it seems now you do).

Bruno