Needless to say, a replacement is long overdue. Just one problem: Asus wants $90 for a new battery. And that's not at all unusual: I've seen laptop batteries selling for as much as $150. Crazy!

Fortunately, I know where to go to find cheap laptop parts: eBay. And, sure enough, with a little searching I found a U6S-compatible battery for just $37 shipped. The seller has an excellent rating, and the battery comes with a three-year warranty. Score!

Your mileage may vary, of course--there won't always be such killer deals for every laptop make and model. Also, I should note that there's a bit of a safety risk involved in purchasing cheap, third-party batteries. On the other hand, even manufacturers' own batteries have been , so you might as well save a few bucks.

Batteries aren't the only laptop part you can find cheap on eBay. As I wrote back in 2009, . I did a five-minute surgery on a Dell laptop, which had sticky keys and rubbed-off letters, and spent a grand total of $12. The result: a laptop that looked and acted like new--keyboard-wise, anyway. Again, your mileage may vary.

Finally, if your laptop screen is cracked, burned out, or otherwise not working, look to eBay for an affordable replacement. Prices and availability definitely vary widely here, and replacing a screen isn't nearly as quick and easy as replacing a battery. The seller may offer instructions, or you may have to do a little online reconnaissance to find help. But even if you hire someone local to do the labor, it'll probably end up costing you a lot less than the manufacturer would charge.