Hi how much price of iphone7 plus back body

It will depend on what damage the Apple Technician will find, and whether or not, you still have an active AppleCare+ plan with it. Since it's an iPhone 7 it, most likely, is out-of-warranty.

You can double-check, what coverage your iPhone still has, here:

• Check Your Service and Support Coverage - Apple Support

As far as potential costs, check here: iPhone Repair & Service - Apple Support

think the only iphones they ever offered to repair the back of are iphone 12 and newer

but you can check iPhone Battery Repair & Replacement - Apple Support

or reach out to their support channels

Apple Support

And or

Contact - Official Apple Support

and or

Genius Bar Reservation and Apple Support Options - Apple