I've never purchased brass. I started collecting my spent casings about a year before I bought a reloading kit. When I go to the range, I scrounge the brass buckets. I also have some friends who save their brass for me.
Unless you're reloading obscure calibers, there's no need to pay for brass.
Let me know what calibers you reload, as I pick up brass indiscriminately and mail out the calibers I don't use to people who can use them.