Titleist Thursdays are run by Titleist reps and it is just another reason to buy Titleist. Unlike a demo day of multiple brands and a lack of individual attention. For a full bag, you're taking 2 hours of a trained professional's time. You can check with the pro shop, they will share the rates for you. Also check how much of a discount you get with a purchase. I've generally had the fee waived with a purchase of what the fitting was for.

The Celtic Manor is local to me, they are a National Fitting centre for Titleist, they charge £50 per 1/2 hour session, I believe they refund half of that cost when you purchase the club you've been fitted for.
I watched their staff go through a session when I was there on a Titleist Thursday, of the two I'd have to recommend the Titleist Thursday session. Tim Baker, the Titleist fitter had better product knowledge and used Pro V1 balls rather than range balls to see the true performance, it was a good 45 minutes session and free with no obligation to purchase from any retailer, which meant I could look around and get the best deal.
IMO getting fitted by a recognised fitter is a must I don't think I'll purchase another set of clubs without doing so again, so the cost is well worth it in the long run.