I visited Phanom Rung on the way back from Isaan recently. It was early morning- around 7.15am, so no crowds about. And you escape the heat of the day, as theres a fair few steps to climb.
Still 40 bht for farang, 10 bht Thai. Phanom Rung was actually built as a Hindu monument, not Buddhist. It's on the peak of a dormant volcano, so some nice views over the surrounding plains. I only took a few pic's, as the camera battery gave out.
Pretty good view from up here-
Our only company was a mangy stray dog that followed us everywhere, but he was friendly. Well worth a visit, and plenty of other stuff to see around there too.