Hi
The cost of AppleCare+ varies by country. In the US, for example, it currently costs $129 for iPhone 7 Plus:
However, keep in mind that, if you were to buy AppleCare+ now, it would not cover pre-existing damage.
The screen on your iPhone is covered under Apple's Limited Warranty against defects in materials and workmanship, but not against accidental damage.
Apple advises that you should not continue using a damaged iPhone. Follow the instructions here to arrange for your iPhone to be inspected and to establish your available service options, timescale and cost:
- US: iPhone Service Answer Center - Apple Support
- Elsewhere: Apple - Support
Apple's screen repair price (if that is all that is required) for iPhone 7 Plus in the US, for example is $149 plus tax and, if required, shipping: