just to clarity, you're going to use someone else's business model, which you've almost got a website for, yet have absolutely no way of 'economical' (read: cheap) production? you've certainly put the cart before the horse, eh? 
dunno. seems plastisol transfers won't be a perfect fit once you break the costs down, assuming your shirts are going to be under $20. screen printing is out. you'd probably want to sublimate mugs, and that's a different process. overall, just for shirts, dtg is the way to go, imo, yet you don't have the money for it. indeed, i can't think of any other way of doing it for what you're wanting. what you're wanting is based on doing high volumes of individual sales and thus required a method to do that economically, and that's why they use dtg.
just my opinion here, but it's best done with dtg machines, else i don't know if i would pursue this particular kind of business for what you're wanting.
dunno. seems plastisol transfers won't be a perfect fit once you break the costs down, assuming your shirts are going to be under $20. screen printing is out. you'd probably want to sublimate mugs, and that's a different process. overall, just for shirts, dtg is the way to go, imo, yet you don't have the money for it. indeed, i can't think of any other way of doing it for what you're wanting. what you're wanting is based on doing high volumes of individual sales and thus required a method to do that economically, and that's why they use dtg.
just my opinion here, but it's best done with dtg machines, else i don't know if i would pursue this particular kind of business for what you're wanting.