I just had a similar dilemna. I switched from Apple (5) to Android (HTC One M8) 18 months ago to save money after I smashed the 5's screen and didn't want to pay £120 to get it fixed. The 5 used to cost me about £45 per month ($70ish) and the M8 costs £33 ($50ish), saving of £216 over this period ... however, I hate the damned phone and the OS. The size is too big, the OS is buggy, and basically it's been nothing but trouble.
My network wants me to upgrade but in Apple it only offers the iPhone 6s and 6s Plus. The Plus version is way too big and the standard size is way too expensive.
Solution: I picked up a reconditioned unlocked Apple 5s for £250 ($400?). I'll use it without a SIM as a WIFI only device until my M8 contract is up, and a will then get a SIM only contract I've reserached for £12.50 a month, including more data than I have now.
Basically, I went back to the phone I loved all along and I'm going to make it last as long as possible. May seem mad but, I had the original 2G iPhone for 5 years before getting the 5.
Hopefully can make the 5s last until the iPhone 10, hahaha :D
TLDR: If you want an iPhone, there's nothing wrong with the 5s. You can have basically the same experience as having the 6 at a fraction of the cost.