Okay, for those of you with too much spare time, and $20-30 dollars to spare here's a pretty cheap way to make a very nice OGRE board. Keep in mind I haven't even attempted to try and make a "GEV" board yet, but I'll let you know when I do. I'm currently finishing a 40" x 40" board, but my first was a 24" by 44" miniatures scale version of the original, well loved barren wasteland from OGRE.
If you are finicky, or want really smooth terrain, sift your sawdust first to get the chunks out. I didn't bother. In the bowl mix 3 parts glue, 3 parts sawdust, 1 part water. aproximatly. mix and add more of whatever you think approriate until you get a nice oatmeal consistancy... it'll probably actually look like oatmeal. Great! Spread this gunk all over the board (I did mention do this outside or on newspapers right?) Try to get an even coverage. You may notice it's not sticking (needs more glue and sawdust) or it's clumping (needs more water and glue). Fiddle with the mix till you can get a nice even spread over the board. You don't want it thick, in fact you want about 40-60% coverage. When you are satisfied put in a well ventilated area and let dry. This will take a while... like a day or two if it's humid.
Okay this is the most dangerous step of whole process. Remember that scrap 2x4 I mentioned? Take that and scrape your newely dried board. Hard, don't worry the woodglue has bonded on there pretty strong, all you're going to do is basically sand it. So you don't scrape your self while playing.
Okay, make some more sawdust, glue 'n water mix, this time with less or no water. Get yourself a cup of water you don't plan on drinking from, and a spoon. The spoon is for getting globs of goop outta the bowl. Dip your fingers in the water regularly so that the goop doesn't stick to your fingers while you're molding it.