Playing Lite: Robinhood
In this campaign frame, players take the roles of Merry Men, followers of the outlaw Robin of Sherwood. As the campaign begins, the PCs receive word that Robin has been captured by the Sheriff of Nottingham and will be hanged. It is up to the Merry Men to rescue him.
The first adventure consists of the PCs infiltrating the castle, fighting their way past guards, and reaching the tower where Robin is held. When they arrive there, however, they discover that Robin has already been executed. The Merry Men then make a narrow escape and retreat to Sherwood.
Their leader dead, the Merry Men fall into despair. That night, the spirit of the forest appears to the PCs (perhaps in the form of Robin's ghost) and tells them that they must take up the Hood and become the new heroes. The spirit grants a boon to each of them, a supernatural gift that complements their natural talents.
With this blessing, the PCs can take the fight to the Sheriff and continue Robin's legacy.
Begin by making 125-point characters. These are experienced outlaws, probably among the highest-ranking Merry Men, but individually, they are not the action hero Robin is. You should allow up to -50 points in disadvantages and up to -5 points in quirks. It should be obvious what skills are or are not appropriate to the setting.
The Merry Men are Struggling Wealth at best and should be Status -1 to Status 1, depending on how lofty they were before becoming criminals. The campaign is Tech Level 3 (Average starting wealth is $1,000), and as unsettled outlaws the PCs get all of their (adjusted) starting wealth for equipment. Armor is available down to Mail on the Armor Table (p. 18), though no PC can start with better than Leather. All Melee and Muscle-powered Ranged weapons are available, with the exception of Rapier.
After the spirit gives its blessing, immediately add 25 (or even 50!) extra points to represent supernatural gifts. Point costs don't change, but you can give the new traits a mystical flavor in description if you like. Examples include increased attributes or dramatic bumps to a few key skills. Just about any advantage on pages 8-10 can make sense as a supernatural ability, though Jumper is obviously out of the question. Luck is especially appropriate.
The first book I would suggest if you are looking to invest a little money in the campaign is GURPS Robin Hood, available as a PDF at Warehouse 23. Only about 1/5 of the book deals with the legendary Robin Hood, while the rest adapts the basic story to other time periods and shows off how flexible GURPS can be.
GURPS Magic can be used with the rules in Lite to turn the game into full-on historical fantasy. (If you don't also pick up Basic Set, you'll need to know that Magical Aptitude, or Magery, costs 15 points for the first level and 10 points for each additional level and adds its level to skill when casting spells.) Some spells do make reference to traits and rules in Basic Set, but you can get by for quite a while without tripping up.
Finally, GURPS Low-Tech greatly fleshes out available equipment. Its companion volumes showcase the kind of historical research GURPS supplements are known for.