Are you using 1/8" wall 1" square tubing? If so, expect to pay about $2.50 a foot for it at a reasonable steel dealer. I'd go with 1/16" thick 1" square tube. It's around $1.25-$1.50 per foot at a good dealer. You may have to deal with a minimum order, though. Keep in mind that steel is a volatile commodity like gasoline. Go a hundred miles and you may see a 20% price difference.

Expect to pay 4 or more times the dealer cost when you buy steel "by the piece" at the box stores.

Also, find out where your nearest scrap yard is and ask them if they sell usable scrap. It's $0.20 per lb here.