It is a piece of string question and one isue is how much you intend to sail (i.e. wear and tear) and where you go. We use kit on our boat 24x7x365. It's said that an atlantic crossing puts the same wear on a boat that an average boat will get in 5 years doing summmer weekends and a few weeks holiday p.a. Also sailing in the sun degrades everything - paintwork, canvas, fenders etc

From that perspective I'd say maintenance is in the region of 10 to 15% with some large extras on top e.g we've had our engine rebuilt, replaced a crappy 3,000 rpm generator, fitted new wind instruments, fitted new autopilot, repainted the boat.