The WearLink straps are very nice, especially the newest WearLink+.

I recently bought one here: http://www.hrmusainc.com/a-strap-wearlink.shtml

< $20 and free shipping.

Edited to add: I just got the replacement strap since I already had a WearLink transmitter. The whole thing is $55.

http://www.hrmusainc.com/wearlink.shtml