I know a lot of people like buying used drives but the ones for sale are usually loud enterprise edition drives which won’t work for me. Should I buy the drives now or wait until BF for a possibly better sale?
HDD prices haven't really moved in any meaningful way over the course of the past years and I don't recall them ever moving significantly even during special promotions (short of pricing errors). I strongly suggest to treat high-capacity hard drives as the luxury consumables that they are and just buy them as needed. Unless you particularly enjoy bargain hunting as a passtime I really don't think it's worth the effort and opportunity costs in this particular context.