Help to fund a motorbike engine

Hi I'm after some help to get my son's first bike on the road after he brought it to then be bloked from the guy he brought it from as the engine would not start and when took to the mechanic he said the gears and cam rod and piston was so damaged it would cost more to get fixed than a new engine would my son saved for several years to be able to buy this but I'm not in a state to help him at the moment due to be let go from work after a serious accident so I'm looking for help to get him a second hand engine so his able to ride it and get out and about and meet new people where he has autism he finds it hard but has a passion for motorbikes so please help many thanks