You could run 700c wheels and just run a long reach caliper. Probably no more then $40-50 for a set of long reach Tektro calipers and have more then enough room for some knobbies. Just another option. Then pick up a Megarange freewheel like a 14-34 6spd unit for cheap. I've got a Schwinn World Sport in my basement I was going to convert into a CX bike but then I had canti mounts brazed on for 700c wheels so I don't have to mess around with calipers. Too many projects and not enough funds to finish them all.