Perhaps a minor detail, and correct me if wrong, but I thought all Midshipmen received the same pay. My recollection is that is 1/2 the base pay of 0-1. However, USNA collects all pay in a funny money (I am sure there is formal name for it) account used for uniforms and sundries like haircut, tailor shop, cobbler. etc. What the Midshipman actually sees varies by class year.... I don't recall when the change occurs., seems to make sense that a 3rd Class on summer cruise/Protramid now would need more cash than they get during the school year ...but of course there is some advantage to keeping them poor so they don't go out and get into trouble.
As an aside, reason number .... that NAPS is a great deal. I was paid as an E-1/E-2 while at NAPS, and coming out of High School in the Midwest, getting paid every other week while all room and board were covered was quite a luxury. We spent a fair amount in Newport, but saved enough that I never really had to think about money until I had a car first class year.