Surfboard Buying Guide for Beginners: Finding the Right Board Under $100

Question
I've never been surfing in my life, but it's something I want to try.  The problem is, I don't know what kind of surfboard to get and my budget is probably under $100. I'm aprox. 5'1 110 (with little possibility of growing... I'm 17 :) but I'd also like my sister to be able to practice on my board, if possible, and she's about 4'10 170 lb.  I would like to know what brand I should get, what height, what variation, and from which retailer?

Answer
I've never been surfing either,  I'm a windsurfing expert not surfing. Windsurfing equipment if very different than surfing but I am sure there are many surfing experts here at All Experts you just have to make sure their topic is listed as surfing, not windsurfing.