uhh, it's been said before but find a nice rail somewhere, get a hacksaw/cordless angle grinder, a pickup truck and some partners in crime and steal one then weld on supports...
go to a shop teacher at school or to a local garage/welder. tell them what you want to do and i garentee they will want to help and it will be prettyy cheap.
yea my school (like many) has a whole room with crazy tools and stuff, and the teachers can always get hooked up with good deals. my class might even be building one if we have time at the end of the year