Prize pot maths

They keep saying X person leaving has cost the group £30k, as if that's coming out of all their money.

If they currently have around £250k in the pot, then they'd currently each get around £25k at the end when it's split.

So X leaving is only really costing the group £5k, and you may well expect they'd have spent more than that in the rest of the trek, so it has saved them money really.