Hey Kilted you might be able find a 24" wheel cheap - it's a standard on bigger kids' bikes, think of a 10 or 12 year old. However it won't likely have a disc compatible hub, so you'd be stuck for brakes, but if you're talking about welding then you could get a pair of v-brake mounting posts relocated on the Free Radical to allow them to work with a 24" wheel. Xtracycle's kickstand is pretty slick and fits into their system such that I doubt you'd be able to replicate it for less than just buying theirs. Not to say you couldn't make a center kickstand that would work but it's not going to be like theirs. There's a guy in Seattle that makes the be all and end all of cargo bike kickstands, but it's even more expensive than Xtracycle's, in fact they sell it. Lots of pics on this site:
http://rollingjackass.com/
Good luck with your build!