Bottom line is you can't just get a Top 10 QB any time you want. A guy coming off the best year of his career, with a ring, and in his prime is gonna command this type of dough. I'm sure it'll look like a bargain in a few years, just like Brady's contract and Peyton's contract probably looks like a bargain now.
It COULD look like a bargain, but to compare him to Brady and Peyton is dumb, its more likely that they will end up looking really stupid in a few years when Eli pushes out only mediocre numbers, but is still pulling down 15 mill a year.