I agree, sell the tiller seperate. In my experience you usually just about give away implements when you package them with a tractor. A good used 5' Tiller could bring $800 or so.
The big issue you have is that Kioti now makes tractors for BobCat. They are in a pricing challenge and you can get them new with a loader for not much more money. I priced out a 35HP Bobcat last summer, cannot remember the model but it was the large chassis one not the small chassis, New Style Quick Tach FEL, R1's as special order, HST and it was in the $15,000 range with no haggling.
I would think I would try for $12,000 and see if you can get anyone to bite but in my area I would guess its about a $10,000 tractor tops.
Chris