haha, okay, this is like medical care and I would suggest if you are anything like me (I am in the -6's and have to be constantly wearing my contacts or glasses) that you not be a cheapass when it comes to glasses. I've bought both cheap lenses/frames and cheaper contacts and both turned out lousey.
If you're paying low price now for glasses, you may find you have to go back in six-eight months for a new pair, at which point you're paying more.
basic rule of thumb is if you're going to be wearing these for hours and hours and hours daily for the span of at the least a year or two, don't go somewhere that has them done in an hour...it's your vision, not a pizza ^_^