At a recent club meeting the subject was tools, and folks brought in their best or favorites. One guy bought in some neat clamps he paid 8 bucks apiece for. Someone said the local Harbor Freights had a very similar clamp for a buck each.
I went there and picked up three of these things. They are "bar" clamps, about six inches long. These are the kind you press a button to make large changes in size, then press a "trigger repeatedly to build up force. The teeth are VERY fine, meaning you can control the clamp pressure very nicely.
I have not tried it on a model yet, but they should work a lot better than any other clamps I have, and the price was right!