Main motel/hotel is the Thunderbird next to park which also has food. Others are in town, not too far away. Get there the afternoon before to drive the rim and take a look. You need a high-clearance 4wd and the skills to drive through sand, water, quicksand at times.
Guides are (were?) at the HQ and are by the hour and are first come, first served. Never have had a bad guide in the 4 times I've gone through the years, including the time we were caught in the flash flood and came out the following afternoon...with a guide on her first trip. Spectacular!