After serching the webby I have found the cheepest place to get mesh is ebay. Just serch for "aluminium mesh" or you end up getting a load of underware I found mesh for abour £5.50 in 30cmx55cm peices.
here in the philippines. All mesh are too cheap. better to go here. if you want it. lol. in 2$ you have 7x7 feet
acctually if your looking for grill type mesh, you can get some disposable vegitable grill things at the local grociery store for like $1 (its about 1'x1' maybe a bit bigger) they're made to cook your vegitables on your grill but their acctually nice and very cheap too, but if you need bigger they wont have anything bigger then that but for $1 you can get a bunch of them
there is a radio hobby store where i live and they have small sheets of brass mesh. punched round holes for a $1 a sheet approx 1' x 1'. Its for shielding RF equipment