This sounds like one loose spoke. Try plucking the spokes around the worst point of the rim's deviation and see if you hear one that sounds too low or just makes a thunk instead of a ping. Now, I am guessing you are new to wheel truing so DON'T address this yourself before a big event! Like posters above have said, this is probably a quick fix for a pro and he shouldn't be charging you much.

But long term - seriously consider developing wheel truing skills. So some day when you show up at an event and the wheel isn't perfect you know what's going on. Best way to learn this is NOT on those nice wheels but a set of regular wheels with lots of spokes. Regular 32 spoke wheels; the kind that work well to train on. (A caution - you might end up like me and loving the process of buildingl your wheels! I've bought 3 wheels in the past 50 years that didn't come on bikes. Two at Performance sales where I wanted the rims and hubs and they were cheaper with spokes than without. A front wheel at a shop I volunteered at where at the end of a full day of re-habbing wheels, we could have any front we wanted for $10. 25 wheels to chose from. 4 of us. Fun!)