[DF] A party's Ally?

[A Ladder]

My players typically hire a healer when adventuring (as they typically don't play Clerics). This campaign they have really enjoyed their pseudo-Druid hireling and wanted to purchase him as an Ally, but as a group.

Is there a rule of thumb for the entire party paying character points to get one joint ally?

I effectively just figured out the point cost as per an ally and then divided the CP cost among the players. Is that the best way to go about it?