You didn't specify whether you need it in a small 2.5" factor that can be powered by USB or a larger 3.5" version. Price on the former is more expensive.
I have a Western Digital 1 TB that I bought for around $100 about a year and half ago and use it just for backup. It works great and I have never had any trouble with it.
$54.95 per year, or drop $100 today, and never pay a cent for storage again.
If you factor in the internet fees and the electrical costs (assuming you can determine how much your computer uses per month), it'll get really expensive, really quickly.
If you can snag a LaCie drive in that price range, go for it. Otherwise Western Digital mybook is a safe bet. Seagate vs. WD = Western digital with a very slight advantage in durability and consistency.