Amazon does have price caps on books submitted through their Kindle ePublishing system. The max price is pretty high, actually. But that's obviously different from charging a reasonable price. I assume that Evans either understood that his market was small but dedicated, or he figured that he could release it at a high price and then lower it as time went on. The third option is that he's a self-absorbed narcissist who knows jack-shit about marketing and sales and tried to rip off his audience because that's what he does. Who knows?
I do think that there is a bit of karma in knowing that so many people got the book as a free download. Maybe Deborah Dykstra could have offered bootleg copies of it for a small fee?