I agree prices are high but it is Broadway where they're always high for the hits.
Secondly what this singer doesn't realize cuz he's nowhere near as successful is Bruce isn't making much doing this. Using round figures the place holds 860.
860 x 500 = 43,000.00 per show
The theater gets its rent and a percentage of the production.
Even though it looks like Bruce doesn't have many expenses compared to a concert. There are still quite a few. If anyone scans the playbill you'll see what I mean. Security, the union staff at the theater, Bruce's management team, Bruce's regular's of which 35 are listed. All of them get paid and I don't think they're working for minimum wage.
Anyway, the point I'm trying to make is Bruce isn't doing this for the money.
IMHO, it's the challenge of trying something new. Bruce is not afraid of a challenge especially when it's within his own artistic purview.