I've been kind of going through this dillema myself. I think it's actually cheaper to swap cogs. you'd be hard pressed to fine a $26 track chainring. that is, unless you're using a 3/32" chain in which case you probably have a bunch of chainrings lying around already.

If you have a lockring tool then it's a piece of cake to change your cog. you can just do a reverse rotafixa to get it off. or if you're chummy with your LBS just make them do it for you (or show you how).