Domains cost ~$7-8 wholesale. So if you bought it for $4 just keep in mind that the registrar, as a business, has sold that domain to you at a loss and therefore is going to try to earn back that money whether through renewals (and making it difficult to move away) or otherwise.
Also because of that, they consider once you register then you're a client. So nobody is going to have $4 recurring. It's only going to be $4 for the first year.
The absolute wholesale cost of a .com is a few bucks more than that. If its a promotion they are either eating the cost as a branding play or the renewal is 30ish bucks next year to recover the cost. Of course you can transfer it but the time spent doing that may just be worth paying a normal rate from the start.