For $500 is get this an be happy!
What size frame should you choose?
Choosing the right frame size goes a long way toward enhancing your riding experience. Unfortunately, different manufacturers measure their frames in different ways - so a 19" frame from manufacturer A may vary wildly in size from a 19" frame from manufacturer B.
Frames are commonly measured in two ways: from the center of the bottom bracket, along the seatube, to the center of the top tube (called "center to center"); and from the center of the bottom bracket, along the seat tube, to the top of the top tube (called "center to top"). You'll need to determine how the frame you're interested in is measured to determine the proper size.
Mountain bikes are measured in inches, while road bikes are typically measured in centimeters. The right frame for you is one that is small enough to allow proper standover height, while still allowing the seat to be raised high enough for athletic pedaling.