Hi - I've just got to share this with all of you. Today I went to a welding supply shop and bought a tube of stainless steel "tig rods" for just under $16. The tube holds about 25-30 1/16" rods, 3 feet long, which is more than enough for blocking my largest afghan. They came in a nice, heavy plastic tube with a loop at the top for hanging!
Also, I stopped at Lowe's and spent another $16.88 for a big package of those snap-together floor mat tiles (the ones for kids with letters of the alphabet) that will make a perfect base for stretching the afghans on the rods and then pinning them down right into the mat tiles.
For under $32 I'm set to block almost anything. So maybe go hang out at your local welding supply shop, too!
PS - If you need flexible stainless steel wire for blocking curves, they also sell that. It's a very large spool of wire, though, so you might want to divide the wire (and the cost) with other knitting friends.