I'm going for it, using these tires from Northern Tool and Equipment for starters:

http://www.northerntool.com/webapp/wcs/stores/servlet/Produc...

12-1/2" OD x 2-1/4" section OD tires on 2-1/2 w. molded nylon hubs/rims for $7.99 USD each. I bought the wheels today. The rims seem stout enough. The tires are the typical cheap knobby tires on kids bikes, the bearings are junky ball bearing cartridges. I'll probably go get some sealed cartridge bearings after I get them built and tested. I hope to get them built this weekend, next week at the latest.

Chris Krumm