I recently attended a retreat that was led by a lay teacher. While the cost of the food and accommodation was a set cost, any payment to the teacher was by dana. The teacher gave a very inspired talk explaining that Dhamma is not part of the orthodox economy, but part of the economy of the gift (dana) that was central to Dhamma and which can never have a price attached, as I'm sure most of us are aware is because it is essentially priceless.
This is an excellent example of how teaching the Dhamma needs to be approached IMO. By lay teachers making people aware that they survive by dana, you will find most people are more than willing to give generously, and importantly it enables people with limited funds not to be excluded. Once a price is put on Dhamma, it's on the slippery slope to becoming a commodity and losing it's purity.