As an alternative to paying £300 - 350 for a Campervan pass (current eBay price) I have discovered that you can use the Rugby Club in Crickhowell (opposite the Park/Ride point). They would charge £15 with hookup (3 free spaces) or £12 without hookup (unlimited space). If there is demand they might open the loo/shower block for an additional fee. The Park/Ride runs every 10 mins at peak times and every 30mins at off peak. Lawrence Watts is the contact - lawrencewatts99 (at) gmail.com. I have his phone number, but won't post it publicly here.