Right now georgiacopper.com has a 2000 foot roll of awg 14 bare solid for $189. To me that's expensive. You'd think bare would be cheaper than insulated but it usually isn't. I use awg 14 solid insulated and it has worked okay now for about 14 years. I got it in the 500 foot rolls from big box stores like Home Depot but when I bought mine it was around $14 / roll. I think now it is up there around $33. The reason why insulated is cheaper is simply that more of that wire is made than the bare stuff and the big retailers probably take less of a markup to compete in the free market. You pretty much have to go with copper if you want your ground system to last. That electric fence wire will rust out on you pretty quickly. Ditto for barb wire and any other steel or aluminum wire hams often use. Insulated material other than copper wire may work but to be honest, the best way if you ask me, is to just bite the bullet and pony up the doe re mi and do it right from the get go and enjoy the results rather than futz around with insulated steel mesh and so on. Solid copper insulated or not, is easier to work with and bond in with the ground system common point. Aluminum will decompose in some soils and anyway, you have to deal with bonding aluminum to your common point via brass, it can cold flow in a clamp and so on, i.e. it has some problems. One thing you can do initially at least to save money is do a lot of 50 or 60 foot long radials instead of half that number at 100 or 120 feet. Let's say you have 2000 feet of wire. It would be far better to have 40 fifty foot long radials than 20 at 100 feet. Another thing to avoid are snake oil ideas like "tuned radials" (essentially at grade radials with loading coils) or something called "the folded counterpoise." Wire on the ground simply collects and returns currents to the feedpoint, is entirely detuned by earth proximity and "folding" or "tuning" does nothing.