I've never heard a thing about Excalibur, but when comparing rates, make sure they're offerring the same things as Tanisha (my favorite) or Searious (who offer a similar trip).
Tanisha includes a light breakfast, lunch, soft drinks, then excellent rum punch and beer on the way back.
Tanisha even had rain slickers for everyone the time I went when it rained while at the ruins.
You really want a guide who is very familiar with the area and knows where all the birds and animals live.