If you have a dvd burner you can use it to backup the drive. A 100 pk of blank dvd's typically can be had for $20-25 and would give you just over 450gb capacity. Pla on spending alot of time doing this.
Windows has built in utilities for creating a backup or a system image and can be found by clicking start and searching for 'backup' and clicking on 'Backup and Restore' from the results.
Alternately you might be able to find a decent deal on a usb external harddrive. Check your local store sales ads. 500gb is available locally here for $60, 1tb for 90 and 2tb for $100