The one basic tool that everyone agrees is indispensable and not easy to substitute for (as many others are) is a concave cutter, which is used to cut branches flush with (or actually very slightly concave to) trunks or bigger branches. You won't find them at any hardware store, and I think most of us buy them online through big dealers (Dallas Bonsai Garden, Bonsai by the Monastery, Brussel's Bonsai, etc.) or through local clubs that may place a big order for supplies and get a better price for members, or at local bonsai stores if you're lucky enough to have one. An 8" long pair is usually the best size, and while you don't need to spend a lot (though you can) on a pair though they may last you forever, I wouldn't necessarily go for the cheapest of all. Wire should be copper (annealed) or aluminum, and it's hard to say which size to get as it depends on whether you're growing big (if trunk-chopped) trees or tiny ones, but almost any good book will give you the info. on proportions. I rarely use wire except to anchor trees into pots, and have forgotten that myself!