[Baalz]

And another angle to consider is the loss in income from the province, not just the upkeep of the mage. Particularly because the more blood hunting provinces you use, the less and less ideal they are - as you start wanting more bloodslaves you start bloodhunting in higher and higher population provinces. The more concentrated your bloodhunters are, the cheaper the bloodslaves (not even taking into account defensive considerations)

For instance, consider two different ways to go using LA Abyssia as an example. Lets say I'm bloodhunting with 2 B4 Abysian warlocks. Lets also say for the sake of argument, that not only do they have SDRs, but they each also have one blood booster which was forged for summonings/forgings and is not being used this turn, so they're effectively bloodhunting at B6. Extrapolating the trend shown in the graph (and that each blood level is supposed to gain you +1 slave) those two bloodhunters are going to pull in 14.6 + 6 = about 21 slaves per turn.

Alternatively you're using sanguine acolytes with SDRs because they seem on the surface to be more cost effective. Nice, cheap, holy blood hunters. Thing is, to get 22 slaves per turn you need 4 of them (plus the same boosters and an extra rod). Problem is, you can't put 4 B2 bloodhunters in one province or the unrest skyrockets. How's that upkeep difference looking as you switch extra provinces over to bloodhunting? This can be an enormous difference if you (for example) have a bunch of wastelands with a few high pop farmlands. You bloodhunting yet another 10k population province, or would you rather have your hunters spinning their wheels in a 3k mountain?

BTW, this is also the real cost in bloodhunting with scouts. Their upkeep is usually cheap compared to the lost income from the province they're bumbling around to eek out a handful of blood slaves.

Oh, also those two extra castle turns to crank out two extra bloodhunters (Warlocks vs acolytes) are not worthless resources.