If you are set on terrain tiles this advise won't work, but consider going the route of a nice terrain mat - either painted canvas (about as cheap as you can get and still get something that looks good) or find one of the tutorials here on LAF for a mat using a caulk, paint, sand, and glue mix (maybe some flocking). Sure, you can't do depressed terrain features directly but you can build hills and such that match the mat and go on top of it and get pretty darn close.
Canvas - a paint drop cloth from your friendly neighborhood box store, same source for a few colors of their cheapest latex interior paint (don't let them upsell you, cheap here is best!), and some cheap brushes - and maybe a roller and pan for the first coat. This does not need flocking but there are ways to enhance if you like, such as grass tufts and such but then you might not be able to roll it up so easily.
If your budget is too tight for flocking, get hold of some 'clean' sawdust and dye with basic RIT dyes from the grocery store (one very messy job, invest in rubber gloves!!!!!!)
The canvas mat option is cheap enough you can eventually own several with some painted to match specific battlefields.
Good luck!
