I was worried that hair extension prices might be a little too high for my college budget, but I found lots of stores with over 100 human hair extensions available. It was really nice have so many options.
I use double sided tape hair extensions. They are real hair and take more care than the synthetic ones -- but they look nicer to me. I can get ones that match my hair texture and thickness so they blend right in.
I avoid the funky colored ones, but I can see how those would be fun if you wanted to add some color to your hair without permanent damage. I know that they are very popular among high school kids – probably because they're so cheap.