Caribbean Cruise Question?

Question

I'm going on a Caribbean Cruise in March. The excursions range from $40-$700 and I won't be able to afford one each day. If I don't go on an excursion can I just get off the boat and walk around town? I would like to get off the boat and stop in local shops and restaurants to get the local experience without paying so much money. Also- does anyone have any info on free beaches you can visit?