I just happen tp have the payroll sheet for SHOWBOAT from the week ending January 26, 1929. Chorius members were making $20-25 pw --- thats about $300-350 in todays $. A small supporting role - 'Rubberneck' - earned $50 a week - about $775 today.
So the multiplier is roughly 15. If you were paid $100 in 1929, that equals $1,500 today.
The ranking of pay rates on this show is interesting. Helen Morgan, who played Julie, earned $700 (this was 18 months into the run, mind you); so did Sammy White who played Frank. Howard Marsh, who played Gaylor Ravenal, was earning $1000 a week. Norma Terris, the Magnolia, was earning $1,250. But the biggest star in the show was Charles Winninger (Capn Andy) who earned $1,500. Jules Bledsoe, who played Joe, earned only $400.
The casts were huge up into the early 60s (with the exception of WEST SIDE STORY) because musicals still had separate singing and dancing ensembles.
More interesting is that 18 of the 22 actors on the pay list were part of the opening night cast. Besides the 22 principals, there was a 'white chorus' of 24 women and 16 men, and a 'colored' chorus of 16 men, and approx the same number of women.