I have long argued that Amtrak should be offering Slumbercoach, Section, or both as a "second class" accommodation, offering a bed, but not a meal. There should be a less luxurious option between coach and private-room sleeper. Amtrak did offer Slumbercoaches for a while there. If the Amfleet Is get replaced, I bet they could be converted into some form of section sleeper. 18 sections, 36 individuals, although you could sell the sections as double-beds if you are a CLOSE party traveling together, I guess.
Viewliners hold a theoretical (2 per roomette, 3 per bedroom) maximum of 33, but its only sold to one party, so they probably on average hold more like 25 "sold out". This could offer 36-54, depending on whether you can get people to double up in lower beds. But figure that they'd hold about, oh, 40 people "sold out" verses 25.
Superliners? Lessee, you'd need an Accessible room. And then you get 6 sections on the lower floor, 20 on the upper floor. 26 sections, a maximum theoretical capacity of 80, but a realistic capacity (figuring about a quarter of the lower berths get two people) of 61 people. Versus a theoretical of 49 and realistic of 36 for the Superliner Sleeper, and 75 for coach.
As for how much that would cost, I dunno. $50/night above railfare? More like Businessclass in price.