Peter, I don't know how much experience they'd have on the ROC - probably worth enquiring to the Caddie Master.
The impression I get is that a great caddie can make the Old Course a wonderful experience for the first-time player, but unfortunately most of the ones I've seen out there havn't been particularly good. I never bothered with one because (i) I can't afford it, (ii) I wanted to unlock the secrets of the course by myself in my own time, something which is possible over a year, but difficult in a round or two.
If you choose to take a caddie, go with the £40 option, and speak to the Caddie Master as early as possible to get one of the better ones.