Units with a lower cost of upkeep per man are

Celtic Warriors (swordsmith, Ireland or Wales) (cost 25/100 men)

Other units with the same upkeep per man are
Arbalester
Arquebusier
Crossbow
Gallowglass
Golden Horde Warriors
Highland Clansmen
Jobbagy
Kerns
Nubian Spearmen
Pavise Arbalester
Pavise Crossbow
Slav Javelins
Slav Warriors
Viking Thralls
Woodsmen

Celtic Warriors, Nubian Spearmen, Slav Warriors and Viking thralls all have the 100 man unit size.
Any of these units should be built instead of peasants. The only reason I can see to build peasants would be to fill a crusade or jihad as a roleplay excercise, or for fun (with +1V in Provence with gold armour, gold weapons they should be a little meaner than standard Chivalric Men at Arms)

mfberg