If you guys want a tip from a guy that buys a fuckton of music but never really has that much money, I could provide.
If you truly just want the music, dont worry about first presses of older stuff. Buying newer versions will cut your collection's cost greatly. (and I like to hear old demos that sometimes get stuck on as bonus tracks to re-releases anyway)
Buy stuff you can get for $10 and under first. There exists so many metal classics (and even new stuff) you can get for 10 bucks or less, it's silly. I've only ever spent $20 or more on two cds, Deathcult for Eternity and Conjuration of the Spectral Empire
Dont be afraid of used cds from amazon or ebay. You can get great deals there and basically if they arent in the condition they're supposed to be in, just bitch. Amazon and ebay users know when they are in the wrong and will cough up refunds quick or the sites will make them. I DO NOT LIKE DISCOGS because they offer no real buyer protection other than paypal itself. I've had trouble with nearly every goddamn transaction I've went through there.
Dont be afraid of sellers on UM or metal archives. Sometimes times get tough for fellow metal heads and they dump pieces of their collections for dirt cheap. That being said, ALWAYS PAY WITH PAYPAL AND IF YOU DONT HAVE YOUR STUFF AND THE PERIOD FOR FILING A CLAIM IS ABOUT TO END FILE IT IMMEDIATELY. Dont let a seller string you on until that period ends. Their word means nothing, paypal's word is the difference between your money and being ripped off.
Take advantage of clearances and buy x get one free deals. Just make sure you're buying things you actually want here or you'll end up with piles of junk cds.