trikster2, in my experience, using identical drives is unnecessary. Getting 2 drives that are identical in size is essentially impossible, anyway. The high-level formatting by the manufacturer will leave even 2 drives of the same model as slightly different sizes.
It does make sense, though, to buy identical drives, as you will be bottlenecked by the slower of the two.
Officemax has a 120GB Western Digital that you can get down to about $50 -- after rebate, a $30/$150 online coupon, and a couple of FAR items to get over the $150 mark.