We ate at Primarily Prime Rib last week while vacationing in Vegas.
We had a great experience. The two of us wanted a nice low key dinner after eating/staying on the strip for 5 days. I had the Maple Salmon and my date had the Prime Rib end cut - Cowboy Cut Portion.
For a busy Saturday night around 8PM - service was great. We felt the price for two adults, with drinks included was very reasonable at $55.