My first advice is to ditch the hot wire cutter, and buy and exacto knife and a really thin saw. my favorite saw looks like a heavy duty carving knife with a deeply serrated edge. I can`t say enough how much easier life is with those two. I use the hot wire cutter now and then for specific purposes, but the fumes are horrible, and its slow compared to good old fashioned carving. Heres a list of what you`ll need and how I think you should get it, most affordably:
Insulating foam sheets- The pink or blue kind are excellent, get them in sheets at a hardware store $20 buys you a 4`by 8`1.5 inch sheet I believe
Latex house paint- Get the colour you want the ground of your hill to be, if you dug down a couple inches. I usually go with a shade of brown. This is an item you can get dirt cheap or free. Go to the local paint recycling place and ask if you can have some of theirs. I did, and now have a ton of colors, all free. I also go to the local paint store and buy returned off tint cans, at a fraction of the price. Every bit you can save adds up, when you are making terrain for a class of 30 kids.
Cat litter and sand- pick up the sand when you buy your foam. Use kids playground sand $5 for a bag bigger than you`ll need for the rest of your life. Cat litter from the grocery store, also more than you`ll ever need, unless you actually have a cat.
Vermiculite, pollyfilla and latex caulking- these are optional extras, used to add texturing to your work. Buy them all at the handy hardware store. Vermiculite is a soil additive from the garden section. Its like super light cat litter.
Weldbond glue- Hardware store must have. Great white glue, strong, cheap and pretty quick to set.
Ground cover flocking- I use 2 types, static grass and fine ground foam, both from Scenic Express. Buy from model railroad places rather than 40k stores, your wallet will thank you, as will local retailers.
So much for materials, now comes the easy part.
1-Take your foam and carve it into a rough shape that you want your hill to be. Kidney shape, oval, whatever.
2-I like to use 1.5 inch foam, so I then cut away ledges and details into the block I just cut. I glue some of the cuttoff pieces onto the hill for variation.Alternately, you could pancake layers on top of one another, if you want to build a bigger hill. This works great, but dont get into the trap of just using 45 degree cuts for the whole hillside. Its functional enough, but the appearance is pretty plain next to one you`ve spent a couple extra minutes carving. The terrain will be with you for a while, dont cut corners now.
3- glue what needs to be glued and let it dry
4-cover it all in paint. easy enough, but move onto the next step before the paint dries.
5-add ground texture (optional) If you bought the vermiculite, plaster and caulking, mix up a `goop`of all three with some of your paint and water. make the mix look like really thick toothpaste and you`ll be good to go. Spread it around on your hill, spareingly until you get the feel of how it looks. It will smooth out you hill cuts and add subtle rolling effects to the ground, so its well worth the effort.
6-more ground texture. Sprinkle by hand a mix of sand and cat litter here and there, especially at the base of any steep areas of you terrain, to look like loose rockfall.
Add it pretty thick if you dont want the grass to stick over it. its up to you.
7-grass it up. Again by hand, add the ground foam and static grass. Basically just throw it on. nature is random, you might as well be too.
8-wait for it to dry, turn it upside down, shake off loose material onto some newspaer and save for your next project.
Thats it. Start with a small hill to try the techniques, or you`ll be like me and look at your first one and go `what was I thinking...`