I took advantage of a bit of decent weather yesterday morning to do a loop walk from Portballintrae to The Giants Causeway. The walk along the beach and cliffs to get there was lovely but Mark Twain hit the nail squarely on the head when he remarked that The Giants Causeway is "worth seeing, but not worth going to see". If you do go, it is free to visit. You do not have to pay to go in via the Visitor Centre, although you could easily be caught out. You will have to pay to park. You can park more cheaply at the mini railway next door (£6 I believe) of do what I did and park at Portballintrae for free and enjoy the walk. Might not be so good in full bike gear mind you!
http://www.walkni.com/walks/2557/portballintrae-causeway-loop/