Yes, you are charging to little depending on results.
Most people don't mind paying but they expect to get their money's worth.
On the other hand, $400 is to much if the horse doesn't meet expectations.
In my line of work I don't want to be the cheapest, but rather, the best.
When a customer tells me my prices are high I usually respond with Yes sir they are, and here's why. I then explain the value behind my price.
Your time is what you're selling, and as it's the only thing you have to sell, make sure you get paid good for it.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.