I think it can be a bit of a "catch 22", a lower share price would be for either an older boat which may well then require higher ongoing maintenance costs, (or possibly a newer boat with only "low season weeks available"), or initially pay more for a newer boat which requires less maintenance?
When we first started looking at shares (about 7 years ago), we looked at some boats around the £2.5k for a 12th share and soon realised that we would need to spend at least £1k+ more to get a boat that we liked. We ended up in a really nice self managed syndicate which also saved us around £450/yr each in management fees, however this does mean that all the syndicate members have to take an active role in doing all the work necessary, and as time went on and new members joined the syndicate there were fewer and fewer members who actually wanted to share this level work preferring to leave it all to the ever diminishing and willing "few". We liked to keep the boat well maintained and promptly replace any items that had failed, or were likely to fail so that other members would not lose their holiday weeks. We also liked to maintain a healthy sinking fund (£6k+), so that if the engine went south we couldm get it replaced with minimal financial impact to the existing syndicate members. (ie if you do buy into a share boat ALWAYS ask what how healthy thier sinking fund is as you don't want to buy into a boat that suddenly needs a new engine or £12k repaint and nothing "in the pot" to cover it!)
In some respects the actual buying cost of a share is not really an issue (assuming you have the money in the first place), as you could well get most of it back, particularly in the current climate. (We had members who actually sold their share after a few years for more than they paid for it in the first place), and the longer you are in a syndicate the more "cost effective" it becomes compared to renting. The only rel downside to sharing is that you are always limited to the marina the boat is based in, (which can be moved with agreement from all members), and the fact that the weeks you can choose very much depend on where you are on any particulr years "pecking order".
I guess you pays your money and makes your choice......happy hunting!