How much should I expect to pay for an acoustic guitar setup at SamAsh?

It depends on what the guitar needs. A basic setup starts at $50 but depending what needs to be done it can go higher. Just because two strings are broken does not mean the guitar needs a setup, by the way.

Sam Ash Acoustic Guitar

It's never too late to start learning how to set up your own guitars. I remember when I was about 16, I used to spend about 60 bucks every once in a while to get my Floyd Rose guitar properly set up. Now I do all my own setups saves me some extra cash. Unless its something i can't repair then I'll take it in to a shop. Normally a full setup, string change, truss rod adjustment, string action and intonation will run you about $50.

Not sure what big box stores charge, my local shop charges $40 - $50 depending on what all the guitar needs.