I've always sent mine by Royal Mail Standard Parcels although I've only ever sold individual clubs.
Standard Parcels is ideal for items up to 1.5m long and 20kg in weight, provided the combined length and girth doesn’t exceed 3m. Golf clubs don't exceed the length limit for Royal Mail, as previously posted.
An individual club is well below the 2kg limit so is only £4.41 to send.
So far as boxes are concerned I unravel any large cardboard box, cut it lengthtwise and form a toblerone type tube to house the club snugly with lots of brown packing tape. Wrap the head in bubblewrap and Bob's your uncle. Never had any complaints.