Try a parking app like Spot Hero. You will find the best rate for parking that way and see a map of where the parking garages are and how far away they are from where you want to be.
Street parking is hard to find and still costs money. A garage is a more expensive option but is more likely to be available -there are several around. Definitely would recommend taking the subway or trolley - 15th Street station literally exits right into the park
My recommendation? Take the subway! We did & no regrets!
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