I'm a Pennsylvania snowbird who makes the trip to Florida each winter. When I go to Key West I stay at either Boyd's Campground in Key West or Lazy Lakes RV Resort on Sugarloaf Key (about 15 miles north). I paid $65 a night at Boyd's and $55 a night at Lazy Lakes. I see from their web sites that current rates are $63 at the former and $50 at the latter (and going to $40 on April 1st).
I was at first frustrated that I had to pay $65 at Boyd's for a tiny pull-off beside a 3/4-size picnic table and a pole-mounted BBQ and so close to the next site that I had to parallel-park into mine. On the other hand, I was under a palm tree in very pleasant weather and within bicycling distance of downtown. Showers were fine and they have wi-fi throughout the campground and a laundry.
Lazy Lakes is primarily an RV resort but has about 10 open 'tent sites' around a pond. The road around the pond is narrow and looks precarious but is fine for vans, pickups, etc. The sites are just open gravel and don't have site numbers so campers just kind of space themselves out in the available space. The bath-house and showers are back on the RV side and reasonably clean.
In the Everglades, I've always been able to get into Long Pine Key and Flamingo campgrounds. If you stay at Long Pine Key, don't miss walking around the Anhinga Trail (at Royal Palm visitor's center) boardwalk at night, preferably all alone at ten pm or so (yes, it's ok to do that). Oh, yeah, and on your drive in and out, keep an eye out for panthers. And pythons.
OC