You're quoting prices from three different restaurants!
The cheapest option is the "chippy" near the harbour and I can confirm it does have seating for about 30 people at the exact same price, given I've eaten in there several times.
Inverted snobbery is still snobbery.
It's £12.95 at Rick Stein's, to eat in - a huge bonus with small children, compared to the constant worry about them diving off the harbour wall whilst you're trying to eat.
I'll be there in about 6 weeks.