Thanks for everyone's help!!
Thought I would write a little feedback in case anyone else had similar questions....
We ended up just driving to Benagil and hoping we would be able to get to the cave! It couldn't have been easier, just followed the signs to Benagil, then right beside the beach there was a girl selling tours to the caves. We purchased a 30min tour for 12.50 Euros. The boat fit about 8 guests - but everyone else must have purchased a 1 hour tour because the trip was much longer than 30mins. It was a great tour - MUCH better than the cave/grotto tour they offer in Lagos.
The girl we bought the tour from said they had 3 different boats and captians - two of them being Fernando Cabrita and Ruben. Our capitan was Fernando Cabrita and he was so great - I can't believe the caves we fit into (I would be sure to check tide times, I believe these tours are better during low tide)
We were mainly interested in the big cave that you see in all the pictures, and it is literally just left of the beach (east). You could easily swim there from the beach...we didn't realize it was right there until we were on the tour
If we were to go back, we would like rent kayaks. There are so many caves with beaches to explore....but we wouldn't have known this if it weren't for the boat trip first!!
Highly recommended! Bring your camera