How cheap are you talking? I would at least look for stainless spokes and an aluminum rim. If you can't afford that on a new wheel then go used.

As for 700c the problem is that the brakes often won't reach the rim. Some people have gotten it to work using longer reach brakes, but unless you already have the wheels or brakes it will be cheaper to just get 27" wheels.

http://www.niagaracycle.com/about.php have a lot of 27 inch wheels. Maybe call them and tell them what you have and let them recommend something.