Depends on your use of the phone. From what you are saying, you have a budget restriction, in which case, as other people said, it would be better to buy a decent used one. About the 5s itself, it is a great phone and you should have no problem. There are many people who do not like large phones and I am one of them. I have been using the 5s and bought 6 when it came out, but returned it in a few days. But I am a gadget freak and always have to have the latest and greatest. Recently, I could not resist the urge and bought a 6s, but I think I will be returning it soon. I use the phone mostly for communication and PIM, and for that purpose, you can't beat the pocketability and palm-fitting 5s (it's the perfect size and very light). Yet it is fully capable of browsing and content consumption It's just smaller. You should not worry about the obsolescence for another 2 years or so. Apple is running out of additional features and they will be more into new external design, screen, ever increasing CPU speed or gimmicky features etc, but I do not play along with them
. Return to basics, so to speak. Don't worry, go ahead.
Just my personal opinion.