It's close on the cheap end, but if you can get that USB to SATA/IDE cable for less than $20, then you could pay less for an internal than an external.
Tigerdirect.ca listings show that a cheap internal is about $45-55 CAD. A cheap external is $70-75 CAD.
If you compare prices of the most expensive/large drives: 1TB internal hard drive by Samsung is $304.99, a Kanguru BioSTOR 400GB USB 2.0 External Hard Drive with 40 Bit DES Encryption runs you up to $487.99 CAD.
I'd say that $325 is still cheaper than $490, despite needing to buy that adapter.