Minimal paints... hmm..
Spray brown.. they just came out with a brown spray at
GW.. but army painter, krylon, halfords, some other brand of spray can....
all good. Even airbrush is fine.
Even 100% coverage of whatever brown... so maybe 2 coats
lol
Drybrush all over in a lighter brown.
Ratskin flesh to pick out the tails, noses, hands... anywhere the fur isnt
All Metals warplock bronze, drybrushed leadbelcher.
Pick out claws and teeth with something like Rakarth Flesh,
Wooden parts a different brown to the fur

(grey furred rats might make this easier)
If you want red rags... then pick out the eyes and clothes in red, mayb use a dark grey as a 2ndary clothing colour.
Wash all over in Agrax Earthshade.
- youd get through a hell of a lot of agrax... I suggest buying a bottle of Liquitex Acrylic Ink
Raw Umber, and 60ml Vallejo glaze medium. Mix to desired strength of wash. Itle cost more upfront, but will mix upto a lot of pots worth of the citadel ones. (citadel washes are quite nice however... just for an all over wash of a horde army like skaven... bulk might be a good idea)
Im counting a brown spray and 9 colours there? Add in an off white, like pallid wych flesh to make a round 10 colours, use the off white to mix highlights out of all the other paints
Maybe do simple drybrushed highlights, quick and dirty

the drybrush highlighting of everything isnt going to win any contests

but this is a horde and youve got to think about the time involved doing a well blended paint job times hundreds of very similar rat men.... for me.. dry brush wins in that scenario everytime!