Over $40 for something that just converts is a pretty large amount. I get there are other features of the plan, but having no alternative plans is just ... There is no way to even test it. I also just noticed the price went down to $29 now, which is more reasonable, but even so I'd argue there should be alternative plans that maybe doesn't include the full support etc. I'd assume most people won't need to take advantage of that.
I could probably setup something similar in a couple of hours, I mean there's no magic done here.
Parsing markdown is easy and I already have that as a part of my web-framework.
See: https://github.com/DiamondMVC/Diamond/tree/master/markdown
You might not be the target audience. Regardless how many open source libraries or even products exist, there will be a market for users who prefer a single-click install with support.