Replacing the Screens, Speakers and Charging ports on Nexus 7 2012 and 2013 is pretty easy and you battery is fine. The cost is about the same $45 on average for the Assembly LCD + Digitizer because the are glued together.
Here is what you will need
1. Hair Dryer.. I use a Cheapo $10 one from Wal Mart
2. Guitar Picks I use "Orange" .60mm
3. Small screwdriver set.. included most of the time
4. Patients.. the 2013 model has more parts to take off.
Never buy the Digitizer or LCD separate thinking you can use one of your original parts, they are Heavily Glued together. It's possible to separate them but it will be a major pain in the ass, I do not recommend ever trying this as the LCD is very easy to shatter..
LCD Display Screen Digitizer+Tools Assembly for Asus Google Nexus7 2nd Gen 2013 $45
http://www.ebay.com/itm/LCD-Display-Screen-Digitizer-Tools-Assembly-for-Asus-Google-Nexus7-2nd-Gen-2013-/171734869541?pt=LH_DefaultDomain_0&hash=item27fc322625
2012 Model.. none on Ebay available with a US seller at the moment from China it will take 3 weeks.
Nexus 7 (2013) Screen Repair & Disassemble
https://www.youtube.com/watch?v=hAlNuGrGDuU
Nexus 7 (2012) Teardown Review
https://www.youtube.com/watch?v=xZL1mly7rZ0
Prices as how I have seen them, I buy broken and bricked Nexus 7 2012,2013, Kindle Fire HD or better, Nook HD and Samsung Galaxy Tab 1,2,3 7 inch on Ebay quite often.
2012 Cracked screen but usable Average price $40
2012 Cracked screen but unusable Average price $25
2013 Cracked screen but usable Average price $60
2013 Cracked screen but unusable Average price $40
2012 Nexus 7 Resell Average $75
2013 Nexus 7 Resell Average $100
Cost for you to repair $45-$55
Cost for a new tablet of decent quality $140 and up