I've seen a lot of different numbers for fuel costs per pound but most are recent costs. Rumor was that Alan Shepard had a six iron head attached to some kind of rock mining shaft, but for simplicities sake and to not have to deduct unknown shaft weights, what would be the fuel cost to smuggle an average 1971 six iron and 2 golf balls into space?
In this particular case, the extra fuel cost was zero. The rock collecting probe that the head was attached to was already factored into the total weight calculations. The club head would have been counted as part of Shepard's 5.5lb Astronaut Preference Kit. As NASA supervisors were aware of the makeshift club, and he had permission to perform the golf shots if everything went well beforehand, there's no reason to think that it "cost" the mission anything in weight penalty.
If you're interested in just the raw cost, a Saturn V could lift (roughly) 260000 lbs to low earth orbit, at a (very rough) cost of $3.3 billion per launch in today's dollars. That works out to about $13000/lb.
According to this comment thread, a six-iron head weighs about 260grams, which is just over a half-pound. So in raw lift costs, it would be about $6500 to use a Saturn V to get that head to low earth orbit. Golf balls cannot weigh more than 46grams, which makes them about 1/5th the weight of the club head. That works out to $1300 per ball.
So, all in all, for slightly less than the annual cost of a membership at Augusta National, you could lift a club head and two golf balls to LEO using a Saturn V.