MultiSite Signup Page and Formidable Pro?

I need an answer based on your experience.
I cannot find a way to make my premium template run with a sign up form that will be placed in a custom page of my choice.
Been testing Buddypress but I had error, been trying the method to create a custom sign up form and place it on a page with anti-splog plugin and following some threads here without success.

All I need is a sign up form that is fully integrated with wordpress core functions, easy to customize and to place in any page AND that will not cause any errors issues with my theme (U-Design Theme).

That seems to be a real challenge!
So I went to all the threads here and many people are using gravity forms with Pro Site. But ended using gravity form only with PaypaL. Some were using the membership Plugin with Prosites and were able to make a custom form using both.

Others were able to just create the sign up form and place it on any page using buddypress minimum installation. But if your theme is not multisite or buddypress compatible it can be an issue.

So I need THE solution. Formidable Pro seems to be the life savior. Or am I wrong?
Gravity Form looks also excellent but the price is too much for just a sign up form that works!