[willy]

Price will be based completely on condition of boat and power along with equipment, trailer etc.
Do a search on the site for your question concerning the off shore use. Been discussed many times.
Good weather window the V20 and 21 will handle it fine. But take into consideration that our V's were not built to be off shore boats in the stricktest sense. They are in-shore all around performers and they are one of the best ever designed for that purpose. That being said there are many who use theirs regulary for off shore work do to the sea keeping abilities of the hull. Many go off shore with boats not as well desigend in my opinion as the V's.
They will get you home in conditions that are daunting to say the least and they are famous for doing just that here in the east where I live.
Good luck with your search, but if your intention is to go off shore long distances on a regular basis my advise would be to get a twin engine hull at least 23 feet long with large sea boat type scuppers in them and equip it with all the safety equipment including epirb and life raft and the fuel stoage ability to use the 2/3 rule of there and back with safety margin.
That is truly the only way to be safe as possible for long distance fishing.
Twenty miles is not long distance but weather windows should be your mantra.
JMHO