Nashville International Airport (BNA)
The Nashville Airport is about a 75 minute drive from the Farm (Bonnaroo), so it's quite a hike. We personally like taking advantage of the official Bonnaroo Airport shuttle, which takes care of all of your transportation needs for Bonnaroo and is only $60 round trip. If you are planning to camp then you will likely be renting a car at the Nashville airport, but if not go with the shuttle.
Your cost of the rental car or the Nashville Shuttle provided by Bonnaroo will cost you $60 round trip.
Generally the cheapest time to book flights for Bonnaroo will be about six weeks before Bonnaroo. This means you should be focused on booking your flight in April 26, 2018. This may seem late to you planners out there, but statistically it's the cheapest time to book flights. That said, if this is too late for you book it earlier. One final note is that plane tickets for Bonnaroo tend to skyrocket about two weeks out, so certainly don't wait that long to book a Bonnaroo flight.