There is a few reasons for the price(s) dropping. Not only for BDs by the way, but also for Albinos, Boesemani and other nice rays. Just about 2 years ago Albino pearls went for 10k+ a pair. Now you can get a pair for a third of that, or even less.
This is coming from an European standpoint.
1) Supply and demand. There is simply so many professional breeders and people that have a few pairs at home breeding as a hobby - supply is VERY high.
2) Asian imports. They are cheaper and since most of them aren't pure, they have good looks aswell. Why would you pay 1500 for a pair of nice looking BDs when you can get a pair of even better looking (BD hybrids) for 800?
3) Quality. I know a few breeders in Europe that still breed very high quality, 100% pure BDs. They still demand a pretty high price per pair, but overall the prices have come down for the non-highend BD.
In Germany, you can easily get yourself a good looking (good quality) BD pair for about 600-800 US dollars. Not like AAA grade, but A or A+ grade for sure.
I have seen a few breeders that can't sell their pups at all, because they ask for lets say 300-400 bucks for a non-highend BD and nobody wants to pay that. No joke.
I even know one who stopped breeding his Pearls, completely. He doesn't let his Pearl males come near his females - simply because supply and demand is so bad, he would have to sell the pups for 100-200 bucks a piece and he doesn't want to do that.