Here's the scoop, man. This is what I did. every Sunday, check your newspaper ads (Best Buy, CompUSA, Fry's, etc.) and look for rebates. Be patient. You won't find these rebates at Internet-only places (trust me--I've looked

). I picked up a 120GB Maxtor with 8MB cache over at CompUSA for $60 after a $40 instant rebate and $40 mail-in rebate.
Also check this site out:
http://forums.anandtech.com/categories.cfm?catid=40
Those are good folks. When you hit one of their posts, make sure to check the date on the first post, because some discussions continue after the sale is over.
Admittedly, you'll be hard-pressed to find a 50 cent per gigabyte sale, but I've seen a lot of 120GB drives for $80 lately.
Also keep in mind that Western Digital has a 3-year warranty on all their 8MB cache drives, while everyone else is one year.
Good luck and keep your eyes peeled!