Hinnom (EA, no mods): Ba'al's or Melqarts

[Soyweiser]

But then you hardly save gems. (10 gems for the matrix, + 3 * 2 gems for communion teleport = 16 gems, the coin is 20).

Edit, and the slaves also need to be s3, or they cannot teleport. Not a lot of nations have 3 spare s3 mages

[Shangrila00]

S3s'll also die. With 4 slaves, each will get 200 base fatigue, but it's a S8 spell, and the slaves will be absorbing fatigue at 3+1(LotNS)+1(PotS)+2(communion)=7. Unless you hand out boosters to each of the slaves, you'll need S4 slaves and waste a turn casting PotS to keep the slaves, and nobody has enough S4s to use as slaves. Better idea just to use expendable S1s, expecting them to die, but that's not really cheaper than just shelling out for the boosters, nor can it teleport.

Really, with Master Enslave, you can either go gigantic communion to soak up the fatigue from repeated casts, or use single casters taking advantage of the fact that a caster cannot drive himself over 200 fatigue. Small communions just don't work.