20%? Have I been stiffing the guides?

Say a trip costs $1500/ea for a week. That's $3K for DH and I. There are 2 leaders. So I should be giving $600 to each leader? Really?

In the past I've heard $3-5/day/guide, but that would only be $70/leader ($5*7days*2guests) and that seems way too small.

One tour company said 10% of the cost of the trip split between the guides. That comes out to about $150/leader from 2 guests. I usually use this as my minimum, but usually its about $2-300/leader from the two of us. That's too little?