Thornes' of Wragby, near Lincoln U.K., sell Apidea mini nucs, which
are made of some kind of expanded polystyrene. Thornes have their own
website, so you could look up prices and so on direct. Apidea
originate in Switzerland. I talked to a bloke who had 100 for his own
queen rearing unit, and he was very happy with them. He said you fill
a bucket with nurse bees from several hives and then dose each mini
nuc. with two or three hundred workers, leave them shut up in a cool
place for a couple of days, and then introduce the queen cells. There
is a chamber inside which can be filled with sugar syrup or candy for
feeding the workers. Of course I've met others who disagree entirely
and would opt for a larger size of nuc. A breton beekeeper in the
local press built his own mininucs rather bigger thasn the apidea, as
he had a few failures with the apidea and considered them too small.
My informant with 100 of them was in the south of England, so
temperature may  be a critical factor.