Hair Extensions? What are the best kind?

I'm considering on getting extensions. I'm 14, and I'm going to put them in myself with some assistance from my best friend. (Please don't tell me I should get it done professionally, I know what I'm doing). I want to get them from Sally's Beauty Supply. Black ones that are about 14" or 18". My hair right now is is a little past my chin. I would like to know which ones one would be the best for me, I don't want CHEAP ones, or really expensive ones. I want ones that are reasonable priced, and last for a very long time. Anything. I would like opinions. Just give me thumbs up on some that will work. The reviews on the site DO NOT HELP! So you guys help me out. Thanks Bye!♥