New ones sell for around $1K (with warranty). Used ones for around $750 - saw a few in Singnet classifieds.
I upgraded from the older non-USM lens to the USM lens and I feel it is the best $1000 I have spent. The lens is flawless in every respect. AF rips. This is the ONLY macro lens I have seen where you can use AF in real time for macro work, with moving subjects. It is that good. There are some moving subjects I simply could not have shot without the AF.
It makes a great portrait lens and a nice one for street photography. It is compact, fits into my Lowepro waist pack. Great choice.
BTW get the hood. It does help reduce flare. But expensive - $60+ I think.