VO5 Hot Oil Treatment Two-Pack, approx. $4
Hot oil is the most effective and cheapest hair conditioner - you can either buy it at the store or use oil from your kitchen. For a quick treatment, I use VO5 that comes in a two-pack for about $4 that you can find in the shampoo aisle. All you have to do is run it under the hot water in the shower for about a minute and then put all over your hair before you shampoo - but SKIP YOUR ROOTS. Otherwise, you'll end up super-greasy on top, so just to be sure I always try to avoid putting oil past the top of my ears. Wait a few minutes while you shower, then rinse and shampoo.
If you'd rather just use oil in your kitchen, or for a longer, deeper conditioning you can use extra virgin olive oil or canola oil. Some people like one better than the other, but it differs for everyone. For medium-length hair, try putting a little more than 2 tablespoons in a bowl and microwave for about 10 seconds, but just enough so that it's warm. Then put it in your hair (this part can be pretty messy) and make sure so focus on the ends. I like to leave it in for 1-2 hours so I wrap my hair in a hot towel or saran wrap. Saran wrap isn't too attractive and can be pretty tricky so I'd stick with the hot towel!
Personally, I think that extra virgin olive oil/canola oil conditions a lot better and you don't need to condition after shampooing it out. Just make sure to skip your roots!