I think we are on the same page here. Going from a stressed member to a non stressed is not a new engine config, so no
major cost there. I did state that changing the V (a new config) would cost a lot, especially with the 6 engine rule which means that the engine not only has to work, it also has to be reliable.
The cost for auto manufacturers & bike manufacturers, large or small is approximately similar, it's just that the large ones have far larger profits due to the numbers they produce and so can afford to spend some of that on engine design.
I currently work for JaguarLandrover (a small manufacturer in comparison to Ford or VAG, or even BMW) in Powertrain and we are designing & building 2 new engines at the moment, based on the same block - an I4 petrol & an I4 diesel. Designing and building the first donks, whilst not cheap, didn't take too long or cost the earth.
The hard and expensive parts are a) refining the design to be reliable enough for mass production so as to minimise the warranty costs and
getting it to meet the extremely tight emissions laws. Neither of the latter two things are required for a Ducati motogp engine, but the 6 engine rule does mean that they have to do at least some of the work required for a), hence my original comment that it would not be an insignificant cost. It would, however, cost nothing like what it does for a production engine that can be sold in today's markets.