For rifle targets you'll want steel of 500 Brinnel hardness, AKA armor plate. 1" being a good all-around thickness. For pistols mild steel is fine. I've been using 3/8" flatbar for the flags on my pistol target that sees hits from full-house .44 mags and they hold up ok.
You may be able to find a local welder who will weld up something for you. The hard part will be locating a steel supply shop that will sell you the steel in very small quantities and not a whole sheet without charging you some high dollar extra fee. This is the problem I ran in to, but my solution was to buy whatever quantity I needed to and use the surplus material to fabricate targets for sale.
A simple design for a rifle target is a 1 foot diameter steel swinger. It's a simple target and being a swinger it doesn't need to be reset. It will provide an audible clang and motion when hit.
The steel and the welding rods are cheap. The costly part is going to be the welder's time. Given the weight of the targets, I wonder if there would be any cost savings to order one that needs to be shipped vs. just finding a local welder and finding out what he would charge. He may even have enough scrap laying around.