If you have access to a garage, i recommend MDF (medium density fibre board). Any handheld power saw with a brace / jig on it will work.
Saw = 29.00 at target. MDF = 6 bucks a sheet which is 4 x4 at Home Depot.
Be sure to wear a breather mask when cutting (mdf dust is not healthy to breathe in).
Take the sheet of MDF and trace the rough pattern you want for the base (buildings look nice on square type bases, whereas ruins and other "natural" terrain look better on rounded or oblong shapes). HINT: for easier cutting, if you're cutting a square shape, then use one of the straight edges. Makes for less cutting. If doing a round shape, try to have one of the round edges touch a side of the MDF so you don't have to do a massive cut in to get to your shape.
Use the saw to cut the part out. Take a really sharp utility knife (hobby knife is not going to cut it), and bevel the edges.
Use a rough grit and then a fine grit sandpaper to sand down the edges to a smooth finish - this will also nicely obfuscate any imperfections in your saw cutting.
After that you can mount your building, ruins, etc. any way you want - carpenters glue works best for adhering things to MDF, though any glue will work. After that, water down some PVA and sprinkle some sand on whever your terrain feature doesn't take up space. When that's dry, use same glue + PVA mix over the sand to seal it. Once dry, its ready to drybrush and static grass / flock etc.
Very easy way to knock out some nice quick terrain. I made a ton of terrain for mordheim games this way.
Best part about MDF is it will not warp unless you leave it exposed to saturation for a long time. Particle board and chipboard will warp with any humidity in the air (which, being in New England is pretty much unavoidable).
