Thanks for all your prompt replies, you guys are awesome
I am looking for a flat board I think - I like the idea of PVAing sand etc and then doing a painting exercise.
But as I was typing this I paused to look at another mat pattern in the store that has cobblestone mats: http://www.deepcutstudio.com/product/wargames-terrain-mat-3-x3-badlands-theme - I think this would be a good, cheap starting point and the Old West MDF buildings will look at home on it.
I will have to mull this over until payday - but once again thanks for the replies...