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.
Some do both. It's just really good to see what is offered out there, and to meet the people, and make an educated opinion once you have done that. Smart shopping always wins in any arena.