There used to be free parking at La Railiere on the main road after you have passed thru Cauterets and from there you can pick up a stunning footpath, the route des cascades all the way to Pont d'espagne. Or there is free parking at La Fruitiere in the Vallee de Lutour and that is signposted off the main road
The car park at Pont d'Espagne is enormous And incredibly busy in the summer. As far as i can recall ,as i have only walked through the car park, you pick up a ticket on the way in and pay for the amount of time you have been there on the exit.
As with Martin, i never found a comfortable way of carrying an SLR on long walks. carried on the waist belt it was too heavy, round the neck it bounced about, over one shoulder it slpped off, across the body it interfered with the rucksac, inside the rucksac meant keep stopping to get it out of the bag. in the end i bought a Panasonic Lumix tz60 which is in a pouch on the shoulder strap of my rucksac, easy and quick to access.