It is against the law to buy and sell human organs for transplant. However, a US citizen in need of an organ can obtain an organ abroad for the right price. If legal in the foreign country, would this be morally licit?
The fact that you are referring to ‘buying and selling’ make it morally wrong. Organ donation has its occasions in which it would not be morally wrong but the terms that you place upon it would make it so, I think.
It really depends on the organ. I would talk to a doctor or specialist and ask them what they think. A cornea transplant would is a lot different than a heart or lung transplant.
The wrongness or lack thereof would not depend upon the differing legalities, but on how the organs were obtained.
Countries that commercialize human body parts are treating human life as a commodity, something Christians are called to avoid.
This would apply as much to a cornea as to a lung, IMNAAHO, since both come from a deceased human being. It is wrong to create a situation where persons might be killed for their organs.
The buyer is also “jumping the queue” with regard to the transplant list, however, I am not at all sure that that is wrong. Money can buy all sorts of life-extending medical treatment. It always has done.