Maybe you could do a bit of market research on other “similar” syndicates, see what they charge to fish their water? And how many members they have? Might give you a better idea on price/numbers.
Don’t forget, there are people who are prepared to pay good money to get in a decent syndicate, especially one with such quality fish, so I wouldn’t automatically assume that “price x” is too expensive…
Also... and this isnt always true... but the more money people have invested in the syndicate, the more likely they are too look after it and respect it (no one wants to pay all that money and then loose their place over litter/unsafe rigs etc)