HP Laser Printers are your best bet, I use several at work (4MV's, 5000's etc) and they are going all day non-stop, one of our HP's has close to 1 million pages ran thru it (A 4500), the rest have all at least 300,000 page counts except for our newest, the 5000 which in 3 months has already printed 24k pages, and registration is still tight on all of them.
In other words: These things are very very reliable, I'm very impressed with them. I can't comment if the consumer level HP printers are as reliable, but I'd put my money on them.
By the way, Postcript is only available on lasers for your price range, to output postscript to an inkjet you'd need a RIP unit or software.
GuruMed