I did a pic earlier comparing some Primes, click to enlarge:
I did some research during a price discussion earlier - retail vs actual cost swings the results in MP-10's favour a bit:
MP-04 - 18,900Y retail down to 12,852Y (-6,048Y) @ Bigbe Rakuten
MP-09 - 17,640Y retail down to 11,500Y (-6,140Y) @ Amazon Japan
MP-10 - 23,100Y retail down to 15,992Y (-7,108Y) @ Amazon Japan
That's 3,140Y more expensive than MP-04, 5 years later.
It's also fairly close to what other high end transformable toys go for:
God Sigma - 24,150Y retail down to 19,800Y (-4,350Y) @ Amazon Japan
Daltanious - 23,100Y retail, down to 16,632Y (-6,468Y) @ Bigbe
Or Macross. The recently announced VF-17s retails for 24,800 and only comes down to 21,800 with discount. It comes with a 2cm tall pilot, and a gun!
Yamato is a smaller company though so we're probably paying a lot because of that. There's too much info that we aren't privy to, that determines how much these things cost, so if i have the money and want the toy (now) i don't dwell on it too much.