I've got one of those little electric tire inflators in my truck. Says 250 psi, but it takes about 15 minutes to bring a flat tire up enough to drive on. For under $10, it's saved my butt many times over the past 10 years or so (seldom buy new tires...).
Haven't seen this stuff in a while, but use to be pretty common. It's call surgical tubing. Some kind of synthetic rubber tubing, very strong stuff, holds pressure well. As kids, we made all kinds of fun stuff out of it. For school, the water-weenie... tie a knot in one end of about a foot length, slip the othe end over the threaded part of the point half of a ballpoint pen. Just shove it into a drinking fountian, lot of water, good range. This it what makes me think it would make good air muscle material
Anyway, for under $20 (maybe more) you could get a compressor and the tubing. Valves will cost you, but shouldn't be too bad. Try some experimental stuff, see what you can do on the cheap. There is a type of nylon rope that is hollow down the middle, might be useful. Also have seen some plastic stuff in cars for protecting wiring, braided and semi-flexiable.