I have to echo what Weirdo mentioned about asking other players about what fighters they may have. With my new BT group here in California, co-founded with Zhaofan, we have been poking at the idea of compiling a list of minis that the group possesses. It would allow someone to post that they are planning to use X mini in the next game, but that they do not own it and would like to know if Y player who does own it would loan it to them for the game. My only problem is that I have yet to paint many of my minis, or they need repairs to the paint or reglued, but hope to have a few batches up and running soon. That might be something to consider with your group.
Of course using proxies has been part of the game for as long as I have been playing. Micro fighters are indeed tiny and if I had any that I could easily access and place next to a BT scale fighter I would. Instead of worrying about price you should first ask people in the group, I am sure someone does own at least a single fighter and would gladly bring it along next game for you to use.