One place I don't recall seeing anyone mention is American Apparel. Yes, they are very overpriced considering they sell mostly plain clothing, but I find that since the majority of their generic t-shirts/v-necks/cardigans are unisex, they are slimmer fit. Designed for all the scrawny hipster boys! Just be careful because the shirts tend to shrink a bit length wise. I have a long torso and am around 5' 7" so if I get a small, while once it shrinks it fits me nicely tightness wise (I like my shirts more of a snug fit), but it ends up getting awkwardly short. I like the slim fit around the arms and the tighter neck because it emphasizes my shoulders to make them appear more masculine.
Another equally expensive place is Urban Outfitters, but if you go on their sale days (certain UO stores have college student sales, plus there's always black friday, online deals, etc.) you can get their regularly $50 flannel button ups for $15. They also carry extra small men's sizes for a lot of styles. I am pre-everything so being able to find slim fitting clothes that make me look like an androgynous hipster boy are great.
I don't have the smallest of hips, but I find that H&M make FANTASTIC decently priced jeans. For about 30 bucks you can get some modern style jeans in different washes. I pass even when I wear my "super-drain" H&M skinny jeans since having the ass of the jeans not hugging mine seems a little more masculine. I seem to pass more when I wear the skinny jeans + my Doc Martens (

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Then, of course, thrift stores are always great for trying new styles and not spending a lot. There is a Goodwill in Stillwater, MN that is near a Target, so whenever Target changes their clothes for a season, anything they don't sell gets donated to goodwill. That means tons of brand new Mossimo and Merona stuff! I have also been able to snag quite a few pairs of Levi's 511s from Goodwill stores. Plato's Closet is a decent chain that can sometimes have very nice quality stuff for decent prices, too.