In reality, some of the new and improved arrangers are being introduced at lower prices than their forerunners. I can't speak for all manufactuers, but take Yamaha for instance: As Gary said, the PSR 5700 came out $3,200 with street price of $2,500.
A couple of years ago, out comes the PSR740 for around $1,400. Granted the board was downsized and lighter (which I think is an advantage), but it had more bells and whistles and sounded every bit as good or better than the 5700.
A year or so later, here comes the PSR2000, a major leap forward in technology at about $2,300. Then the PSR2001 and Tyros, neither of which was priced any higher than the 5700 when it first came out.
Wait a few months after the introduction of most any keyboard and you will start seeing more affordable pricing and some real deals on slightly used models.
Eddie