I have done both. If I am somewhere and have to buy ammo, I get something reloadable. With 9mm, before I had a lot of brass on hand I used a rule...If I could buy ammo like Winchester White box at Walmart, it was 23.99 for 100. Well, they sell their new brass for around 21.99 a hundred, hardly any different
pricewise. Now I have so much brass I dont buy ammo unless I am somewhere I have to. Used once fired brass is way reasonable, and once you have several thousand, you are good. Once in a while I will buy a thousand Starline brass in calibers I load, and so forth.
If you are just starting out, always save your brass, and the brass of your friends who dont reload. Buy a couple of thousand once fired, throw in your own saved brass, buy a thousand here and there to add in, before you know it you will have plenty.
russellc