Perhaps this might be news for you, but you can sell your old iPhone and get some money to buy the new iPhone 7 or iPhone 7 Plus. You even have another possibility: recycling your old iPhone.
Depending on the company or personal buyer, while selling your old iPhone you could get up to a 52 percent of what the device cost you in the first place.
It is important to keep in mind that before selling your old iPhone you should wiped all your personal data so the new owner does not take advantage of that information. Also, gather together all cables and accessories of your iPhone and specify which of these items will be sold with the device.
On the other hand, if you care about the environment, you could consider recycling your iPhone. Apple is known for being friendly towards the environment. Furthermore,it has a new robot called Liam that disassembles old equipment to reutilize their parts. So you can take any electrical devices of any brand to an Apple Store and they will handle it for free.
In the case of certain models of iPhone, iPad or Mac, Apple will provide the customer delivering the old devices with a gift certificate to get discounts in future purchases.
More info Apple