Chromoly can rust. Aluminum usually doesn't unless you're riding in the ocean. Cheapest fix is probably some automotive touch-up paint; sand / clean the area (scuff the surrounding paint up a little), apply a coat, wet sand, repeat. Won't be perfect but it'll protect the underlying metal from rusting.
Of course, if you want that perfect "unblemished" look you're probably going to have to plump for a professional (read: take your bike completely apart, sandblast frame, re-paint, put all components back on). Unless you're looking for an excuse to get a completely amazing custom paint job. At which point I'd recommend finding a good powder coat shop; my mountain bike's (chromoly frame) is powder coated and has held up really, really well over the years.