I made two sets of eight hills for a local store, all they need at this point is some paint to help them match their tables (desert and grey wastes). They're made out of 1" insulation foam glued to tempered hardboard bases with some construction adhesive. I used a foam cutter to put some surface detail on their faces and covered everything with scenic dope (qt of latex paint, 2 latex caulk tubs and a cup of joint compound) for durability before pressing in the sand and spraying them with glue.
There's four bigger (18x12"-ish) and four smaller (12x6"-ish) pieces per set. They were cut out of 2x2' panels, I used the right angle corners so they join up easy and made them geomorphic. By that I mean the bigger pieces can be joined together and the same with the smaller. Also, the short edge on the bigger pieces match up with the longer edges on the smaller pieces. They can also be stacked, so there's lots of ways that you can put them together.
I was also able to cut six bases of scatter terrain per set out of the left over hardboard. No pics of those yet, I'll likely put a few rocks and some brush on them and make trees or something on smaller bases that can be moved around the area and not get in the way of the miniatures.
They were pretty cheap, price-wise. You can make four sets (32 hills, 24 scatter terrain pieces) for some $50, not including paint. They just take some time to put together.