I never really had that problem with lack of clothes cause I've been wearing dude clothes since I was a kid. My wardrobe was a bunch of looser T-shirts, vests, ties, blazer, sneakers, leather jacket, button up shirts, etc. I do have a few girly clothes but it's cause my mom keeps buying them expecting me to wear them. Only thing I'm really changing at the moment is my underwear, cause my mom kept giving me packs of underwear she got on sale and at the time I figured "why go out and buy more underwear?" so I just wore the ones she got me. A few sets I felt were unisex and had a thick band at the top so I figured I just wear them till I get tired of them and get enough money to spend on good ones.
But yes, thrift stores are very good for building up your wardrobe, especially if you can catch a 5 for a $1 or 50% day at your thrift store. But lately, I feel that alot of things I want or care for at the thrift store, doesn't fit me well and I end up leaving there with close to nothing. I've been looking online for cheaper new clothes, and found a few asian sites that have very cheap but great looking clothes. It's even a plus that their sizes are more suited to smaller people so it's easier for you to get nice fitted clothing if you're not as big as American sized dudes. Alot of American sized male stuff does not fit me well other then a t-shirt. But remember, if you are going to order off asian sites, to read over their sizing charts. Alot of times you still have to order one to two sizes up cause their "small" is not the same sized small that alot of us are used too. A small would probably be their Medium or Large. So keep that in mind.