I am very jealous. Can I come with you?
You've probably got a transport map but here's one anyway:
http://upload.wikimedia.org/wikipedia/commons/d/d0/Circumvesuviana_maps.png showing the Circumvesuviana line which connects Sorrento with Naples.
As you've spotted already, Pompeii is a tourist trap and they know it. You're only options are to travel out from Pompeii if you don't like the prices, but in all honesty, at this time of year, the whole of the coast is going to be gearing up for the big tourist rip-off. One way to get a bit of a bargain is to look where the locals get their sandwiches etc - these look like bakers shops but often have seats inside where the locals get a beer and a pizza.
There's a lovely one in Sorrento called Franco's but that's way too far out for your holiday - but there may be similar outfits around in Pompeii if you are prepared to look. After all, the locals have to eat somewhere.
As you're only there for a few days my advice would be to grin, be sensible, and bear it. Watch your change, watch out for helpful people ranging from children to old ladies getting between you and your wallet (literally), and just enjoy the archaeology and the insanity that is the Bay of Naples area.
If you get off the train at Ercolano Scavi, the street going down the hill to the site is lined with eating opportunities. It is also getting closer to Naples and so has some lary people, so again, be aware of you surroundings and your change.
I bet you have a brilliant time and please don't take my comments as negative - simply realistic - this is an area of Italy that is perhaps more deeply flawed than most others but is nonetheless beautiful and fascinating.