Ducting can be rerouted easily enough, it is the access that will determine the expense. If you have an easy to access subfloor, it's just a matter of crawling under your house, taking the ducting away from the register, and then rebuilding it leading to the where you want it and then cutting a hole in the floor. This is in the realm of affordable if you have a professional do it, but it is easily in the realm of DYI. The latter would save you money, but you would have to obtain a skill or two and at least have a basic understanding of what you are doing. If there is no real access to the underside of the house, a floor might have to be opened to do it. That would be expensive and a hassle. Other than that, it is not a major undertaking at all, not unless the vent location you choose is a great distance away.