The only info I can offer is about the Plantronics CS50, a wireless headset. Which works great for me, even though I have to take the handset off hook manually. There is a handset lifter, which triggers off of the button on the headset, but the pair is going to be over your price point.

It's in the 900 MHz range, so doesn't interfere with other wireless stuff like the GN Netcom equivelent. But the battery life is kinda short, and if you're on the phone all day, that would suck.

While verifying info, I ran across this.
The GN 6210, which would be yet another bluetooth headset, but comes with a base unit that adds bluetooth to (supposeldy) any phone. It's their second generation, so maybe some of the obvious problems have been worked out. GN Netcom is the leading edge of this kind of stuff, compared to Plantronics marketshare, and is pricey, but the company president here is a big gadget freak and a fan of theirs.

Here's a review:
http://www.mobileburn.com/review.jsp?Id=1078&source=ARCHIVE

And their handset lifter is supposed to be very good.

--Nathan