New one are as follow
WESTERN DIGITAL 1000GB 3.5" HDD 7200RPM 16MB CACHE (WD10EACS)
9800
SEAGATE
1000GB 3.5" HDD 7200RPM 32MB Cache (ST-31000340AS)
9900
so used one would a be 1-2k less than that
btw if i were you i would buy two 500 gb hdd insted of one big one
(to lessen the risk of data failure)
tw a zaitron was selling his 500 gb hdd a few days back
contact him