I don't remember anyone ever having to pay for this either, especially in the US, as the facilities are all taxpayer funded.
But I would agree with finding the facility you'd like to tour in question and giving them at least 2 weeks notice that you'd like to tour. I was just at the California Capital Airshow at KMHR at the beginning of October, and NATCA had a couple of reps there from NCT (Northern California TRACON - NorCal Approach), which is only 1/4 mile off the approach end of 22L at KMHR, and they even mentioned just giving a call for any tours at least a week in advance, and they'd be happy to accommodate.
So definitely do that, and you'll be good. If you plan on SCT though, be sure to make the drive down to San Diego, as the whole entire SoCal basin is covered down there.
BL.