Light Infantry Mercs (Jaegers) are defeated by 3x their number of Skirmishers/Cassadors/Longbows, or by 1.5x their number of Abus Guns (you'll need 7 unupgraded AG to kill one Jaeger in a single volley, so if you brought 14 Abus, you can kill two then run, and repeat). Also, Cannon and Organ Guns do pretty well in numbers of 4-5 if you can keep them alive (Organ Guns are especially tricky with their low HP, as Jaegers will often just focus fire them before losing too many of their numbers).
Heavy Infantry (Highlanders, Ronin, etc) are defeated by twice their number of Skirmishers/Cassadors and 1.5x their number of Abus Guns. With the Counter Infantry Rifling upgrade, you only need 1.5x the number of Skirm/Cas (who do 54/78 damage to them) or an equal number of Abus Guns (who do 80 damage a shot to them).
Black Riders and Manchu are countered by 3x their numbers of Skirmishers and Abus Guns. Or 2x their number of Cassadors.
Mamelukes can be countered by hit and run with 2x their number of Dragoons or 3x their number of Ruyters/Cavalry Archers.
Stradiots/Hackapells can be countered by 2x their number of Dragoons/Duyters/Cavalry Archers with hit and run.
Spahi can be countered the same way as Mamelukes.
So yeah it can be done, but it'll never be cost effective. Thankfully, while your units are readily replaceable, Mercs are impossible to replace until Imperial age.
"One wants to be loved, failing that admired, failing that feared, failing that hated and despised. One wants to instill in other people some form of emotion. The soul shudders before emptiness and wants contact, no matter the cost."[This message has been edited by Ender_Ward (edited 01-17-2006 @ 11:30 AM).]