Save or spend: Spend
You can find a shredder for as little as $20, but if you skimp that much, the motor will probably burn out on you. While you don't need the deluxe Enron evidence grinder, focus on the $100 mark to ensure reliable shredding for years.
This Staples model delivers all the necessities: crosscut capability (meaning it makes confetti rather than strips), 10-sheet capacity (for those unopened credit-card offers) and the ability to cut credit cards and CDs.