What's inexpensive?
You can bike, walk, bus or boat over to the campgrounds. And yes there is a petting zoo and other FW entertainment over there.
You can tour/explore/pool hop the Magic Kingdom hotels.
Use the exercise room in VWL (free!).
Have high tea at the Grand Floridian. Play tennis at the Contemporary.
Rent various types of boats (bringing back the question of "what is inexpensive?).
Lounge by the pool.
Further afield...
DTD, mini-golf, the boardwalk, water parks. And then you can ...gasp...go offsite. There is a huge outlet mall very close to Disney that I believe you can reach by the proper combination of mass transit (or use a cab). Once at that mall you can then access whatever is going on on I-drive...and even Universal. This part I haven't actually done yet...its on the plan for my next Disney-without-theme-parks-or-a-car trip. But I do know the transit connections exist especially the I-drive part.
Higher in price...
Cirque du Soleil, House of Blues, golf, a spa treatment...and I could be wrong but I thought at least one of the backstage tours was available without a park pass.