its not hard to make themes, let alone taking themes from ipb to mybb.
I personally only sell themes i create from scratch so i too feel this is a cheap dishonest way to make money from others work. Ones i made was a bit better than this and sold them for less than 25 so to ask that amount from converted themes is absurd. But I do understand the work part, so if anything a Dollar per converted GOOD LOOKING theme is more than fair for the work/time you put into it.
And hey, if you're looking to partner up we could create a site together. We make about 10 free easy themes first with our sites link in it, to get linkbacks to our site spread around, then also sell custom themes. You make money off your themes and I make money from mine. Share hosting fee which would be next to nothing, you put your sellfy on your product and i put mine on mine.