Hi Dash-Driver,
I have no number to offer to You, but the costs for the difference training should be way below those for a full typerating. The difference course has far less theory classes, simulator sessions etc - however, some traffic patterns were flown in my company before supervision started.
Another point worth considering maybe: Many companies (mine included) require fresh entrants to pass a type rating (not just a differences course) in their own TRTO, regardless of what rating the applicant may or may not have held before. Should the company You wish to apply with have the same rule, You will have the distinct advantage of finding many things familiar from the -300 in the -400, but Your experience will save the company no money.
Last edited by Tu.114; 31st October 2013 at 13:19.