What about the Droid Turbo? Is that an option? $1 at BestBuy.
I don't see any huge differences between the s4 and the s5. The s5 is weightier and the screen is a tad bigger. Everything is slightly improved.
For $50 it is usually worth it to get the newer device. While the difference may not be huge now, as the phones get older and software changes, the newer devices usually hold and keep up much better than their predecessors.
As for Galaxy vs iPhone - it is a matter of personal preference. Go into a store and try them both out.
And another vote for the Droid Turbo - I've never used it, but I know and love its older (and smaller) brother, the Moto X.