Not everyone joins for money; often, they joined just like that.

I tested it; I tested it with an Archmage, a level 10 diplomat character. Out of 10, at least 5 ran away, 1 joined for free, and 4 joined for a fee. The probability can, of course, be increased; this information is in the game manual, but for non-native creatures, the statistics are as follows. In the skill itself, it says that with expert diplomacy, there is a 30% chance of joining (for non-native creatures; for creatures that make up the hero's army, the probability is higher, potentially reaching 60%. If the army is much stronger, the probability is even higher (as the game manual states, but when I tested it, it was the same), but initially, the army is weak).