This was the highlight of my trip to Vegas. If you're interested in Vegas history, not just spending hours upon hours in smoky casinos losing ungodly amounts of money, the Neon Museum is perfect for you.
Book at least a week in advance though their website or via phone or you might not get a reservation. They take very few people at a time through the boneyard, which helps when you're taking the zillions of awesome photos that you're bound to take. They make you sign a release saying you won't sell the photos commercially or use them on a professional blog, which I can understand.
The tour is $15, they hold two a day most days at noon and two, and some if not all tour guides are volunteers. Kim was our tour guide and she blew us away with the depth of her knowledge about Vegas history. The $15 fee is a donation for which you can receive a receipt for tax deduction purposes. So not only do you get a rad tour, but you're also helping to establish this museum which right now isn't much of a museum. Not yet.
Take water and wear a hat if you're visiting during the summer months - there's very little shade to be found on the tour.
Also, they don't allow big bags - they worry that you'll back up and hit a sign with your bag - so you need to leave them at the museum's office during the tour.
A cab from Fitzgerald's casino to the museum was around $7.50 and we took the Deuce bus back to Fremont afterward. The Deuce (inbound toward the Strip) stops right outside of the museum. It's pretty darn close to Fremont if you're staying Downtown.
If you have even a fleeting interest in Vegas history, take the tour. It's definitely worth your time and money.