I'm afraid that I don't know how to edit my original post - so am posting this correction as a reply.
TUESDAY travel dates FIRST CLASS is only $261.50 Round trip MDW/LAS
Unbelievably there are many seats still available. The fares are a little higher from EWR. The same type of sale fares are also there for LAX.
I've paid more than 261 to fly coach!
Hope some of you others can take advantage.