Hy Ken
Welcome to the Forum.
I would,nt worry to much about weights, look around for anything you can use for clamps, ie, pegs, elastic bands, G clamps,ect in fact anything that you can use to hold materials together, pound shops are always a constant source of building aids, sometimes you need to think outside the box, but it's all good, as Alan says old batteries are good for weight, check out your local alarm company, sometimes they are only to happy to pass on unwanted batteries, and most times they can be re-charged.
Cheers Bosun