Gettysburg is one of my favorite places. I try and get there every couple of years. A few years ago, they finally got rid of the cheesy observation tower and a few other tourists traps that had somehow gotten built on or near the battlefield.
Other than Memorial Day and the week of the Fourth, hotels are generally pretty inexpensive, as is most area dining.
If you go, I highly recommend you sign up for a three or four hour battlefield tour with one of the official guides at the Visitor Center. Even if you think you know everything there is to know, they will surprise you, and if you know nothing, they will teach you more than enough.
Best $50-$60 I've spent on a tour.