I think you're probably looking in the region of £6k+ for this depending on output. Or £600 to sit a decent Honda suitcase gennie on the bathing platform, if you can get away with that as a solution...
Have fitted a few fisher pandas which are quite a good unit, The 4.5 will be big enough for most things, have also fitted a small mastervolt 3.5, both companys supply a complete package if required. The Southampton boat show will be a good time to get a deal.
Probably worth having a chat with Atlantis Marine (Plymouth). I had an EMI Dynamica off them and fitted to my F33 when new(2001). They also have Kohler. Mine's a bit heath robinson (Volvo/Perkins 2 cylinder) but wanted to make sure I could get parts and wanted 5-6 KVA to run 2 AC units and the kettle. It was about £5K. Can't remember how much to fit.
Fits into the centre of the central storage space. Helps stabilise the boat in beam seas with the low weight addition.
Strongly recommend:
1) getting an exhaust that exits under water - to cut out the genset exhaust noise when up a quiet creek
2) There are a couple of methods of generating the mains. One is the old fashioned way like the EMI. The other has more complex electronics. The latter, they say, doesn't work with A/C units motors that well. So you'll need to research that.
We have just bought a Sealine S37 with a Paguro 3000 generator fitted by the previous owner. We contacted the suppliers -Advance Yacht Systems Ltd - in Southampton for some advice etc and the service and reponse we received from them was really great. Their web page is www.advanceyacht.co.uk. Hope this will help.
Regards
David