When I started I got a TON of paying clients by training about 25 people for no cost, I just had them pay me with referrals (paying clients). Works good for trainers who do groups and are trying to build a good client base to launch their biz. A trainer can usually get a full clientel load of PAYING clients from 2 or 3 months of this type of strategy, it works for multiple reasons I won't go into here but the point is it works.
When it comes to what to charge I would go about 25% ( or more ) above what everyone else is charging in your area and make sure that your marketing reflects that. For example, on many of our websites we talk about how we DON'T specialize in being the lowest cost service in town, we specialize in results. When you charge more, you're almost immediately perceived as better.
Most people will happily pay more money if they think you're the best around. AND, the ones who won't pay more money are usually the clients who will give you all the headaches and aren't even worth dealing with in the first place. (late payments, breaking contracts, having the stop training because of the holidays or the economy, only referring friends who can't afford the training either, always expecting a break, overall flakiness)
My two cents