Qualities and Realistic Pricing of Personal Training

I am wanting to hire a physical trainer, and I want to hire someone who is actually a high quality trainer.

There seems to be a lot of trainers everywhere and they vary in price dramatically. Im sure a lot of them are qualified, but I feel that there are a lot of unqualified people who are hoping to make some quick cash.

So my questions are, what should I ask for when selecting a trainer, and what would be a realistic price per month for a good trainer