Cabo on a budget

[My3kiddos]

We won 2 roundtrip airline tickets and chose to go to Cabo in October. We have reserved a room at the marina that had an all inclusive option. We took that option just because it was only $20 more a day and the occasional drink or breakfast will cost that much. We plan on walking most places and we might do a snorkel excursion, but that will be it for excursions. If you have been what are some cheap/free things to do and how much should I plan on dining out per day? I've looked at a few menus and it looks like I will be better off getting pesos before we go because it's cheaper. Am I correct in assuming this?

Also what are have to see things in Cabo? We will probably never be able to go back especially adults only (just me and fiancé are going).