It cost us 300 to do the ring road in fuel. Remember to put a pin on your credit cards before going over, we didn’t and almost had a bad night lol.
We didn’t find it hard to find hiking areas but it really depends on how many days you’ll be there and what you want to get out of it. We only did 1 hike I would say. There were 3 others we thought of doing but they were either closed or didn’t fit in the time line. You can really see a lot by driving, pulling over and just stare at amazing landscape. We were also there just before the summer and not everything was open that went more inland.
Lagoons, we went to the two listed. We attempted to find others via the vans gps but found it difficult or access was blocked.
Campgrounds are everywhere. If you go in summer, past June 1st I think every one is open.