Base rock is pretty cheap since it's completely dry; around $1-2/pound. I got mine from Bulk Reef Supply and MarcoRocks. My LFS
charges $19.50 a lb. unless you by multiple pounds. You should still get a few live rocks though, to help seed your dry rock.
I was under the impression skimmers were more based on the size of the tank rather than what's in it, although I'm sure if you're going reef you will need it. I have a 40G FOWLR
and I don't use a skimmer (although I do have one still in the box lol). I use a PolyFilter Pad and it works really well.