That thrifting advice was awesome, no extra notes from me.
As for other places to go... depending on where you live, flea markets can be really great for more second-hand clothing. Some vintage shops that are usually expensive will sometimes have warehouse sales that are way cheaper. Like RetroStar here in Melbourne. You can also swap with a friend, or search online for clothing swap events in your area!
In terms of buying new... outlets are always more affordable. It's just a matter of looking in the right places, even in shops you wouldn't expect to have "alt" stuff. You can find awesome clothes in pretty unexpected places. I live in a pretty suburban area. Since I learned to take public transport into the city, I discovered that there are near-constant sales happening in shopping centres there. Certain stores are way cheaper in the city than in town, which was a shock.
Finally, my favourite: learn to DIY the clothes you want! It's a lot easier than most people think, especially if you have basic craft skills. You don't even need to know how to sew. Badges, stencils, fabric paint and markers, safety pins, iron-on transfer paper... endless possibilities.
Good luck! :D