As said above, most places do unless you bought your tires from that place. Even if you have to pay for it usually is never more than $15, I know at the local Wal-Mart here is $7. Get it done though, it is worth it.
Unless you can get it done for free, Walmart's probably going to be the cheapest place. The problem with Walmart is that they're always packed... you may need to get there reeeeally early - like when they open. Of course, they may be able to do this in between longer jobs they have waiting. But.... if you have expensive rims, I wouldn't take it to Walmart... just sayin'...
You might need an extra jack to support the car, while you pull a second tire off, unless you rotate your spare in.