Two packs were available - one consisted of the three tall silver figures and the two white ones (which appear to have been cast from the same moulds), the other consisted of the shorter yellow and blue figures and four small silvery robots / aliens / whatever which I suspect come from some sort of anime, and aren't really very useful for my purposes. Total cost was £1.15 each pack plus delivery, £3.90 in all. Given how expensive figures are these days that really isn't at all bad. And while the existing paint is fairly crap, the detailing of the actual moulding is actually pretty good, so hopefully they'll be OK once I get them painted a bit better.
The vendor doesn't seem to have any more, but I think that this proves that cheapo plastic spacemen are still around if you look for them.