Central vacuum parts are not inexpensive, even online. That price is not unreasonable. You can easily spend twice that for a powered hose. Just a regular plastic 8' hose for a shop vac can be $25 at the big box store.
If you can scare up some ends, you may be able to make your own hose if you buy the hose in bulk - that's about the only way that you are going to fine one for less money, unless you stumble across a used one. Try calling around to the local vacuum stores that deal in used equipment and/or central vacuum systems and see if anybody turned in a powered hose on which the switch or wiring has gone bad - that is probably the easiest way to obtain a hose for cheap.
My brother uses a central vacuum and I know he has gone through a couple of hoses already because the electrical part goes bad. A hose like that would be perfect for garage use.