I ran into this myself. I didn't have an issue buying one of the form packages, but none of them did what I wanted, so I created my own.
What I ended up doing was to take the Zend Framework's Form classes and strip out the dependencies with the rest of Zend, and also most of the controller stuff. I then just created a module that defined all my forms (arrays of Form Elements, but with hooks to put custom logic in) and loaded them into articles using the {loadposition xxx} syntax.
I did this under a tight deadline, and haven't been able to clean it up to offer as an actual project. It did work quite well though, and there's lots of code that you can lift from Zend.