Sure they will! They'll attach a vacuum to your wallet to remove the cash first...
Really, if you want more RAM, do it yourself. It's a heck of a lot cheaper, and every simple to do. The only tool you'll need is a very small phillips head screwdriver (jeweler's screwdriver.)
Check out some of the online vendors, such as OWC (Other World Computing) who have DIY videos for such things. They also give guarantees for compatibility and lifetime warranty. Crucial and Kingston are some other vendors who you could get memory from as well.
Right now, a 1G module is around $USD 82 at OWC. I'm willing to bet that it would be far more at the Apple Store.
MD