No minimum fee. OF course as soon as I make enough I will go with worldpay. Everyone tells me the $400 dollar set up fee is worth it.
As far as customizing, why not buy it and pay a php dude to taylor it for you. Not sure what you are looking for but u might be able to use phpBB code for free in order to combine all the functions you want.
Here's why I think it is a coolprogram.
It comes with random banners, option to make your own footer and header and most important...
I registered as a user, bought $5 with paypal, clicked pay and I was sent back to the original page with 1 credit ready to post an add.
Sure it needs some tuning but for the price I like it.