So on a tip from a guy at Gamer's Haven, I gave this little idea a try, and boy oh boy am I happy with the results!
I went to the Hubble Image Gallery (
http://hubblesite.org/gallery/) and selected a picture of a nebula that I thought looked cool. I then went to Banners On The Cheap (
http://www.bannersonthecheap.com/), uploaded the image, cropped it, and selected the size I wanted (3'x3'). Waited about a week, and got this in the mail today:
Total cost with shipping was $32. The banner itself was only $15, but I paid extra to get it here sooner. I'm very pleased with the result! The total playing are is actually 3'x3'; the white space around the edge is just a little extra. It's printed on vinyl, so it should be fairly durable, although it smells a bit like an inflatable swimming pool if you get up very close to it.
A couple of issues, as you can see in the picture above: it does reflect overhead light, although the light is somewhat diffused. Also, up close, the image is a little grainy. But for playing at arm's length on the tabletop, I really don't think these issues are going to matter all that much.
Also, the darker colors (blues and blacks) are actually a bit darker than what you see in these pictures; I guess the iPad camera can't capture all the awesome.
All in all, not a bad investment! I think I'll troll the image gallery for a few other pics that might make a good space battlefield background. Now that I have this one to use, I can probably have the others shipped by regular mail, which should drop the total cost to about $20.
I'll post some battle pics after I play next week.