If you have a friend with 700c wheels, you might want to see if those would fit and if the brake pads can be adjusted to strike the rim. Then you can buy a new set like Alex for about $80.
Otherwise, Niagara Cycle has a wide selection of 27" wheels. Just make sure you get a rear for a freewheel and not a cassette. Otherwise you'll need to spend $30 for a new cassette as well.
http://www.niagaracycle.com/index.ph...er_id=&sort=3a