Don't forget, kids, those plastic sprues cost pennies, not pounds, to the manufacturer. it's only the tooling cost that is overwhelmingly massive. Once you've got the tooling cost back it's all gravy. But it's a question of CAN you get that cost back?
Mantic is doing OK with its plastics because Ronnie Renton used to run GW UK and then the GW Trade department, he knows how to get product into stores including big chain stores and even supermarkets. He knows how to get the punters in. He has the funds to hire people to do all the crappy admin stuff and spend all day on the phones selling to traders. He has investors backing the plastics - and even he is searching for a cheaper way of doing those plastics, hence his 'plastic resin' figures, which are basically the same as the plastic figures we know but produced in aluminium moulds rather than steel, which apparently is much cheaper to tool and presumably means the moulds won't last as long as steel ones.
I personally would do plastics in a blink of an eye! - if I had the cash and thought I had a product that would get it's money back inside a year, that is...
PS The tooling cost is more like £30,000 - £40,000 per sprue, not £20,000 as I understand it. Depends on the complexity of the sprue