Working for a Plastic Toy Company I can assure you that the material (Plastic, no matter of ABS, PVC or any other) is not the expensive part here!
The most expensive part of doing such toys is creating the mould where the parts are injection moulded!
These things are made out of metall, are very heavy, have (occassionally) water cooling and cost up to a few 100K per pc! Depending on the size of it.- the bigger the more expensive. And that is for every single piece like a hand, a wheel or an antenna!
Now you would think doing a lot of smaller parts comes cheaper!?
No matter if you do smaller parts, cost will not go down - you need more moulds!!! And more assembly = more humans = more costs!
However I think Yamato made quite a fortune with the old moulds as the only changes they had where the paint jobs and the heads!
So they where up-using there molds to get quantity, sales and in the end revenue!
PS: If you want to know more about how plastics get in their form PM me!