Depends if you are talking about skiing or hiking. Parking is free in most places and its like $5 to drive your car to the summit. You can find more info on the mass.gov site
If you're hiking, in the summer time you can park in the ski area parking lot for nothing. If you get a reservation map you can see all the different parking spots for different Trails heads all around the mountain and those are also for free. The only parking that cost money is if you are parking at the Ranger headquarters or driving up the auto Road
$5 parking fee to park at summit..rest is free. This is different from the ski resort.
Hiking is free for the trails, at least. Just went there a few weeks back. You pay to drive up to the summit though.
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