buying advice for 50+Ft
There are a lot of good companies that built good 50 footers but few that have made a 50 footer specifically designed for singlehanded performance distance cruising. A 50 footer is a huge boat for someone to single-hand. The loads on the running rigging get enormous and sheer distances make it hard to do things almost simultaneously as is required as a single-hander.
I would suggest that you focus on lighter weight 50 footers and that you probably should focus on more modern designs because of the recent improvements in sail handling gear that is hard to refit on some older designs.
Probably at the top of the list is the Hunter HC 50. This is not you father''s Hunter. Unlike the typical Hunter these are extremely high tech boats constructed using the highest quality materials and construction methods. They have a very sophisticated interior and deck plan design aimed at the short handed cruiser. They carry a lot of storage and water capacity.
Another good choice might be a Santa Cruz 52 but a SC52 will need some refit. Another good option would be the J-160. Examples of these neat boats are pretty rare but the one that I sail on from time to time has been nicely equipped to permit comparatively easy single-handing. A smaller and very expensive option is the Morris 454.
An extreme option would be to buy an old Open Class 50. You can pick these up quite cheaply (under $200,000)and for $100K of improvements you could end with a world class ocean cruiser (albeit with a very deep draft).
I still have to ask, as Capt Ron, quite wisely asked, Why a 50 footer? It make little sense to consider a boat this size for that purpose. The costs are enormous compared to the more usual 32 to 38 foot single-handed cruiser. As single-handers they are hard to handle and the risk of something going very wrong goes up greatly with size.