Nicola,
Yes, I'm on a day trip with three other guys. We've found it works well, flying out from Glasgow on Sqeezyjet, sharing a hire car to get to Coleraine, parking it for free for the day, scoffing a huge Ulster fry and Guiness and then walking up to the circuit. We like to walk about the various vantage points, mainly at the southern end of the circuit as it's less busy, and it's so much easier without wearing biking gear. Cost works out at about £50 for the day, which is not bad.
Roll on May 13 ! (I hope none of the racers are superstitious, thoough),
DB
PS how did the exams go ?. Did you cram for your crannogs ?