Margalef - 2 people and a van is 5 Euros per night at the Dam. 2 squat toilets, some sinks and non potable water for that. By the village, it's 9.50 per night plus 3 for a shower. The guy comes round early morning to see/catch people, many move on to Suirana.
Suirana - we've been sleeping in the very top car park, maybe twenty vans some nights. Near the public toilets in the village, so non of the usual shit and toilet paper behind every bush and it's been a pretty chilled vibe.
Generally, we've been fine parked up anywhere. Perles, Coll De Nargo, Montserrat etc. Suirana seems to be the most relaxed place however. There are people sleeping in their vans down in Cornudella most nights.
Hope that helps.