For my first ever terrain board I made a huge river/chasm piece (had pics on the old site). The intent was to eventually fill the chasm with water effects but have been unable to date. The good news was it was a great 4x4 board. The bad news was that since I only had one bridge, the games frequently looked about the same. The 2x2 pieces are a much better option having learned the hard way. The other option was to take a 4x4 piece of wood and texture it then paint it a uniform color (like grey for example). I did this for a second board and use it as a base for either a grey wasteland or an urban ruin. I used a common paint for the bases of my buildings and the hills I built for the board so it all blends even thought the buildings have their own uniques colors (okay, unique colors of grey). My point? Other than the now-defunct GW battlemat I used for grass, it was relatively cheap; the wood I bought at a major department store for about $10 bucks and the foam was another $10. I used Americana Paint (the cheapest of the cheap stuff you get at Michaels [an American craft chain of stores] so that paint was probably another $5. The sand I got from a nearby parking lot.
Of course it is still trumped by "free".
Throw some pics up when you get a chance!