affordable is very subjective..haha.
What's your dolly definition? Some people refer metal tracks as dolly.
Or you're talking about tripod on wheels? Or full pedestal?
For 'tripod on wheels, check out Vinten Pro-5 with its dolly, or the Manfrotto equivalent (they' the same product, different brand). Slightly cheaper will be Japanese made Libec.
For bigger cameras, check out Vinten Vision 8, 11, 100, etc. with dolly.