It seems hazardous to think of credit card benefits as "free". They are included in the cost of the card, along with a bundle of other benefits. I think it is not a coincidence that the cards which include Priority Pass cost $450 - $695/year.
For someone who wants to give it a free trial, the
U.S. Bank Altitude Connect Visa Signature Card is $0 for the first year, and it includes four free Priority Pass visits.