Get the Nexus 5x (directly from Google). It works on all the US carriers, and you don’t need to sign up for any contract so you can get a good monthly price.
The 16 GB version is 330. It is well worth the 80 above your 250 price limit. I is a phone that will last you 2-3 years.
I just bought 3 of them (for my parents, and grandfather).
Do not get a cheap Samsung phone. It will be nothing but trouble and headache for you.
Source: I develop apps and work in the mobile industry.