I actually hosted a 100 person shower! Try looking into community centers, VFW halls, or if someone has an HOA clubhouse. Typically you can rent these venues for under $100, they often have tables and chairs, and then you can bring in your own food to keep the budget manageable.
I don't live in FL, so can't give specific recommendations, but look at the town/park websites in your area for rec centers and the like or ask on your local board. You might also ask a local board on The Knot, as those ladies are probably more familiar with large group venues.