I am assuming this is for use while plugged into shore power
at a marina.
Not portable but if you have a place for the outside unit these work well. The big thing is to be careful about the condensation
drain which will also be an issue with a window unit.
"Mini Split Air conditioning unit". They also come as dual a/c and heat pump units but I don't think you will make your $600 max that way.
Ductless Mini Splits
I have seen several window type units mounted on the hatch over the v berth or salon
. It takes a little building of a box that becomes the mount and duct to blow down into the boat. Again the issue of condensate needs to be dealt with. If you let it just run off the boat you will need to wash it off regularly or you will grow a green mess on you boat.
What ever you use ask a FL air-conditioning person what to spray on the coils in the salt
. There are a lot of motels on beeches in FL with window air conditioning units. They have a spray that they use on these that works very well. I have two mini splits on my trawler
and used the stuff but I can't find the can right now. Works good and lasts a long time. I think I've sprayed mine twice in 6 years and there was still a lot in the can.