Cost me $20 to get in to the temple site and it was worth every bit. In fact I would have paid a lot more to see this amazing place. Take not people, the area the temples cover is huge. The best way to get around is to hire a tuk tuk to take you to the temples from your guest house and then for them to drive you around the temples all day. This doesn't cost a lot and definately makes the day a lot easier. I think it cost me around $20 for the tuk tuk all day. I arrived at approx 08:00 and only left at approx 17:00. A long day, and hard going in the heat. The temples are beautiful and it's worth obtaining a written guide from somewhere so that you can read about the history of each temple as you visit them. The most magical part  of my day at the temples was when I climbed Bakheng Hill to watch the sunset over the Angkor Wat temple.... Absolutely breathtaking. But make sure you get there in plenty of time because this is a popular attraction and it can get quite busy up there with people hoping to catch the best views.