I'm actually also curious why that 5k pop province is generating 70 income. Either there is an Arena there, or you have very high scales, because it should be ~50 income with even scales.
It's true that we have so far been only focusing on the cost of the hunters, but I thought that was what this thread was for, because regardless of your scales, the cost of removing taxation will always be fairly static. That is to say, within any given layout, 5k pop will represent X% of your income no matter what. Since that cannot be directly influenced in game, the only thing that can be influenced, is what type and how many Blood Hunters are used.
To put it another way, think of your tax loss as "overhead" and your Blood Hunter upkeep as "operating costs". You can directly influence your operating costs by hiring poorly trained migrant laborers (ie- scouts), but overhead is the cost of doing business - you either pay it, or you do not do business.
I think the only time that tax loss becomes a major consideration is, when (this happens to me too often) all of your provinces are either <3k or >8k in pop, forcing you to choose between the less effective, or the higher cost options. Also sometimes I get so "lucky" and most of my ~5k provinces have Arenas and Gold Mines and such on them. Gee, thanks.
Of course, it cannot be said enough - the use of Blood, where applicable, is essentially (nearly always) cost effective. That is, you can almost always do more with the slaves than with the gold, regardless of other factors. The trick is, how easily can you generate the gold that you DO need, relative to your other Blood competitors? The upkeep on your Blood Hunters is a very large factor in that equation, and is magnified by your scales, which cannot be mitigated in-game, and which it must be assumed you had adequate reasoning for.
