The thing that makes bone marrow transplantation so expensive (about € 100.000 a pop in Germany, probably more expensive in the US) is that in the time between killing off the patient's own immunosystem and the donor immunosystem taking hold, the patient effectively has no immunosystem at all. This takes about 100 days right now, during which the patient has to be isolated in an environment almost entirely free of pathogens.
So if you want affordable bone marrow transplantation, you either need to find a way to cheaply isolate someone while giving them a very high level of medical care, find a way to grow a complete immunosystem in a few days, or find a new drug that'll effectively fight off every possible infection in a body with no protections of its own. Oh, and then of course you have to affordably stop the donor cells from attacking the host's body, too. Finding a cost-effective drug to cure AIDS looks a lot more likely to me than any of that happening in my lifetime.
So if you want affordable bone marrow transplantation, you either need to find a way to cheaply isolate someone while giving them a very high level of medical care, find a way to grow a complete immunosystem in a few days, or find a new drug that'll effectively fight off every possible infection in a body with no protections of its own. Oh, and then of course you have to affordably stop the donor cells from attacking the host's body, too. Finding a cost-effective drug to cure AIDS looks a lot more likely to me than any of that happening in my lifetime.