Archer is great for money farming yes, as long as I dont use 2 packs of bodkins.
Horse Archer is a different case, at least every second round I usually paid my horse and at least every rounds my bodkins. I wouldn't ever complain about upkeep as I think it is far too low in general though, that is why there are so many guys with heavy armor and better, only the best weapons and heavy horses (destrier and up).
However if you want to raise upkeep, I say, look at weapons and armor first so everyone pays more and not only the cav.
PS: I already wasted the gold for a +2 Horn Bow.