Graham's right about gettting the materials at charity thrift shops to make your own rig. You can often end up getting a backpack for less than $1 (even free, sometimes) especially if there's some damage to it (which may not even affect the parts you want).Also, folding airport luggage carts* can be modified to make a functional guitar cart.
Come to think of it, I have a large canvas suitcase, with wheels and a handle, which is big enough to hold the bottom 2/3 of my HSC. I don't want to sacrifice that particular suitcase, though I paid only $10 or $15 for it at a thrift shop. But sometimes you can pick one up really cheap if the zipper is broken. You don't need the zipper to work anyway, since you're going to remove the top of the suitcase, leaving, in effect, a FRAMED CANVAS SACK on wheels with a handle. You just slip the HSC in and out, without even needing bungee cords, pull out the handle, and go! You'd even have room for some sheet music, a tambourine, a couple of harmonicas, and maybe a collapsible guitar stand or mic stand.
Genie