4 points: 12 Clanrat Stormvermins, count as Foot Serjeants
2 points: 6 Eshin Gutter runners, count as Bidowers
And I have still 4 points to spend... I'm considering a rat pack of 6 models, but I have no equivalence in mind for them. I'm also considering 3 warpfire-thrower teams, count as Handgonnes again. Last solution would be a new batch of slaves and clanrat warriors, but this would mean 24 additional models to paint... Not sure it's a good idea... unless I consider that Giant rats equal Serfs. So, for the the moment, let us conclude with:
1 point: 9 Giant rats and 3 Moulder beastmasters, count as Serfs,
3 points: 12 Clanrat warriors, count as Foot Yeomen.
And now my first attempt to paint a Stormvermin. Considering the limited equipment, he may eventually join the clanrat warriors.