Is it cheaper to make 400hp now than 5 years ago?

 

Yes. Or at least it hasn't gotten more expensive.

Basically, there has been no dramatic increase in emissions standards in the last five years, and that's been the biggest cost driver in the last couple of decades. Damn near every aspect of design and manufacturing has gotten cheaper - whether it's though the use of computer-aided design/engineering or off-shore component sourcing - and so building damn near any gasoline engine has likely decreased in cost in the last five years.