That is true in mass manufacturing. Older products are usually cheaper because they are past the high point of the "Product life cycle cost Vs time curve."
If I have to make an educated guess this sort of product life cycle curve for the new Formula 1 engine is ridiculously short. There engines are almost protoypes in themselves, they have barely lived long enough of a period, are were many produced for costs to come down. These engines are only one year old and only about 80 engines worth of parts have been made - if that much. I can barely see how a 2014 engine will be significantly cheaper compared to the 2015 engine UNLESS
Caterham use "leftover" 2014 engines that have already been paid for by the other teams that were otherwise going to be museum pieces. It is anyone's guess how many 2014 engines are left over but If what Scarbs has heard is true there seems to enough material to supply Caterham for the year.
We must also keep in mind Renault already has a R&D Budget for the new 2015 engine and in fact the engines in coming years. We have already heard Renault's engine guy say that four customers is not necessary for them to keep profitable, it is actually a bonus. We have seen Cosworth work wit two customers. Whether or not Caterham uses the 2015 engine that expense Renault has already budgeted for and they sure won't mind selling Caterham the engine at lower price if it means they can get more data for development. So yeah.. just saying there are merits on both sides whether selling Caterham the 2014 engines, or against the 2015 engines.