If you're in a big city, just go wherever gay people hang out. Guaranteed to be tons of thrift stores with cheap, 'trendy' clothes
For example, if you're in Seattle...check Broadway.
And in my opinion - aside from suits or similar business atire - Clothing choice should only be based on two things:
a.) Its comfortable
b.) *You* think it looks good.
oh, and fuck paying insane amounts for a pair of jeans if the only reason you buy them is because they are "fashionable" - it just makes you look like a total douche. And the type of woman that would approach me because of the brand jeans Im wearing, is not the type of woman Im interested in. *shrug*