I researched custom arches for my Catalina 310. Fellow in Tarpon Springs, FL, makes beautiful stainless steel arches. Figured minimum $3500, probably closer to $5000. Ended up ordering Martek davits and buying a 135 watt Kyobera panel and installing them myself. Cost less than $2000 altogether, and I love it. The davits I got at Martek.com, and the panel and all mounting hardware at svhotwire.com. John at Hotwire also knows the guy who builds the custom arches, if you're interested.
By the way, if you're motoring along on a sunny day after the solar panel is installed, and your tach suddenly drops to zero, don't be alarmed. Just means your batteries are fully charged, the panel is providing plenty of power, so the alternator just shuts down,( ask me how I know this!).
With this panel in place, we have been on a mooring as long as 12 days, without having to run the engine, even in northern latitudes. Gotta love it!