I agree that excursions are not usually inexpensive to begin with, so on our last cruise (just got back 2 weeks ago), I decided to take each situation separately to see whether we would or should tip the guides. Our big excursion was the day we were at Cozumel, we took the ferry over to the mainland of Mexico for the Tulum ruins excursion. We had a Mexican guide on our bus who explained many things during the 1 hour drive to the ruin site, and who stayed with us during most of the exploration of the site, explaining what a lot of the architectural details on the ruins signified. At the end of this excursion the guide told everyone that he hoped that he did a good job and if we were so inclined, he and the bus driver would happily accept a gratuity. DH and I decided to tip the guide $20, plus a $5 tip to the bus driver. The bus driver was the person who distributed the lunches on the bus and who also served us the drinks. I think the $20 tip to the guide was concidered a good amount by him because he shook my hand and even followed my DH to take shake his hand, and thanked us. We were a party of 4, we had our DSs with us, so we thought $5 per person for the tip was reasonable. I really have no idea how much other people tipped the guide or the bus driver. It's funny, but that's one thing I didn't read a lot about on these boards before the trip (tipping the guides, and amounts). I hope this helps!