With M&M3 out I've seen a lot of M&M2 books for pretty cheap at used book stores. I think if you keep an eye out then you might be able to find a great game in your budget.
Marvel Superheroes - which I think is the first and original superhero RPG - is available online for free from a couple of sources. The sites do not make any statements as to their legality, however, so I won't link them here.
By modern standards, it is light in rules, and asks for players and GMs alike to be creative about superpowers - both in creation and in use in play.
Do you mean first and original by TSR?
For first and original superhero RPG, I think that's Superhero 2044.
For first and original superhero RPG, I think that's Superhero 2044.