You also need to know that whatever method they are using, is going to work with your dog. You may want to ask if they will give you a demonstration. We have no problems in giving one, but other trainers may not. There is no harm in asking though. It is also good to ask the trainers if they have any sort of follow-up program, and if they do, will there be a charge for it.
Price is really a relative thing.
It may end up costing you three times as much, if the first couple of people that you get are not able to get you the results that you are looking for. Results are what you are after, and the length of time the trainer has been training is irrelevant if he hasn't been getting results all that time. Some people have been driving a car for 25 years and still cannot parallel park. Another good thing to do is to talk to people that you see that have a trained dog, and perhaps they can recommend someone. Some people offer classes, and some people only do one on one.