The cost of maintenance is directly in proportion to your skill level and the amount of time you can dedicate to your new pride and joy.
We live on our cat fulltime and do jobs as they arise, if you can earn more in the time it would take you to fix the problem, moral dilemma. The more you can fix the safer you become and the less your costs will be.
Given the age of the boat you plan on shelling your hard earned on expect things to break a lot.
Look around the world web for boats in your price range you willbe surprised at the cost of newer boats in the US and the Caribbean, there are boats around that for the pounds sterling you are prepared to part with will come with a lot less falling to bits(even new boats fall to bits) and a lot less ware and tear.
Our approx costs are 6-9% over 10 years.Some years much less others much more