Why not build up the bikes, sell the leftover parts, and put that money into an account or investment of some sort for their sons college fund. Make good use of the bikes you build up, and if the need is really there when their son reaches college, you can always sell one of the bikes or part it out and put that money towards his college education. You would still end up with at least one very nice bike and feel you were doing the right thing, based on your feelings. I don't know how old their son is, so this is based on the assumption he his not yet of college age.