When I first bought them, they were around $150. For a while they weren't available for less than $200, but it seems the price is a little more reasonable now, back to what I paid:

http://www.google.com/products?q=ARS-2000SU&aq=f

I had a 250 gig 7200 RPM Seagate in one for a while but only because I wasn't using it for anything else. The drive eventually died; not sure if it was because of all the stops and starts (which is why I updated the firmware) or something else, but there's absolutely no speed advantage to a 7200 RPM over a 5400 RPM. On slower machines the rotational latency difference will easily get lost in the noise.