If its all you can afford.. - NCSTAR 3X Magnifier w/Flip to Side QR Mount

First and foremost, it's cheap for reasons that you will understand if you decide to purchase. The optics are poor; even though there is a focus ring, it's impossible to get a clear image of the target, and the red dot will also be distorted. Then there is the QR mount, which tends to flop around, causing poor accuracy. Avoid this thing like the plague, even if it's all you can afford. Save up your money until you can afford better.