With freewheel hubs, you can aways just switch out the spacer on the drive side and cut the axel down.

I don't know exactly how wide of a rim you are wanting, but I just bought a rear wheel set (freewheel) at http://www.niagaracycle.com/s for $28. I was also switch from 27" X 1 1/8" to 700C and have a 12 speed Raleigh with a freewheel. I don't know how much you are wanting to spend, but I just bought my bike for $30 off craigslist and was trying to keep the whole project under $100 (so far success), and just wanting is for a cheap commuting road bike.