I think the Nashbar tires are on sale for $15 each right now. You may want to run a web search on the Continentals to see what deals are out there.
Edit: you can use the same tubes you have now -- there's no seal to break on tubed tires, so you can always swap back to the OEM knobbies if you like.
Good to know! I think I'll check for the Nashbar tires. Have you used them? If so, can you give a quick review?