There was a set of 1/72 scale Ratmen figures done Years ago.They had a good mix and pretty cheap too.
Those were the Caesar ones (shown below with a Skaven for scale; they're based on pennies):


They seem to have gone out of production again (or at least to be in short supply), but there's still a box available
here. Plastic Soldier Review has a breakdown of the set
here (scroll down to 108).
Yes, they're plastic, but they're pretty much bang on 20mm high and they're in a nice, Reaper Bones-style plastic that's easy to convert and paint (you can cut it easily with a sharp knife and glue it with superglue - so it's easy to convert them). It's not like the normal horrendous-to-clean-up 1/72 soft plastic.
A cheap metal option would be the "15mm" ratmen from
Irregular Miniatures. They're huge for 15mm - roughly the size of the old Citadel preslotta lesser lizardmen, though more hunched, or the Nick Lund Chronicle kobolds. This shot, from Irregular's website, isn't terribly flattering, but they're quite characterful and ratty figures:

The Julie Guthrie ratmen from Grenadier (just one, I think) and Ral Partha are very nice figures. They're a good size to use as leaders for the Caesar 1/72 ones (a longstanding plan I have on the back burner ...). But they're hard to get hold of in the UK.