When it comes to the Esenthel engine, it is not $150. It is free to try. The Personal Edition is $150, but you can only make one commercial product with it. You'd have to pay again for each one after that. The Company Edition is $750 and, once again, you can only publish one commercial product with that. And the price just goes up from there.

As you can see, with engines like Unity and GameStudio, you pay once and can produce an unlimited amount of commercial products.