Crazy CAt - I would like to point out that until the price of pewter went up about three years ago, the average Reaper mini was $1.25 per (I'm not sure of the pound conversion, but I know that's only a few pence (50-75??)). If the plastics are cheaper to produce, (Reaper is VERY concerned about price, they appologized for three months when they had to raise prices.), then I would imagine that, yes, they will be cheaper than metal, even with the paint job. Dwarven Forge does pre-painted resins that range from $1.66 per to $2.25 per, the detail is extremely fine (much better than any WotC scult) and the painting is really good for machine paint. If plastics are cheaper to produce than resins (and I believe they are - does anyone know for sure) then I can't see the figs going for more than $2 per, but I would think that the target price would be in the neighborhood of $0.75 - $1 per (in bundels - individual pieces may be a little higher). If the price is much higher than that, then they will need to make the "rare" sculpts just to make any money.
As for what they can and can't make, they can sculpt anything, the naming is the problem. As an example, currently WotC is 'claiming' ownership of the Illithid name and the Beholder, however, the illithid is a rip off of the Cthullu spawn. It has already been stated that 'treants' and 'halflings' were use to by-pass the 'ents' and 'hobbits' from Tolkiens estate.
Dragons are non-propretary due to historical significance, you don't have to call it a "Blue Dragon", just because it's blue and a dragon, but if you would, there is no way to sue over it, it can't be liscenced in such a manor. As for the Demons and Devils, I am unsure if Balor or Pit Fiend are copyrighted, but Winged Demon or Scary Devil are not and of course Succubuss, Eryines and the like are classical Greek monsters and therefore, fair game.
I think the biggest effect these are gonna have is to deflate the prices of some of the 'rare' minis on the secondary market. Especially on certain monsters that were made 'rare' that are game staples, such as Trolls, Umber Hulks and Carrion Crawlers, that can run between $20-$50 for the Harbinger minis. Carrion Crawlers are usually seen in groups, I as a DM am not trying to pay $100 - $250 just for 5 low level monsters; if Rreaper can offer them at a better price, yes, I'll be getting them - if they can't, then I have to stick with the 'open and hope' method.
And as I said before, I'm still wondering if the recent WotC announcements about 'scenario packs' and 're-issues' are the "Oh crap!" measure taken to lessen the blow.