How much does it cost to send into apple to repair broken iPad screen

Cost depends on where you are, something we don't know. For U.S. users, this support page shows pricing. http://www.apple.com/support/ipad/repair/screen-damage/

They may not repair yours; they may send you an equivalent refurbished model that is not broken. This part of the article explains:

After you send in your iPad for service, you’ll receive a replacement or your repaired iPad in three to five business days. A replacement iPad will be new or equivalent to new in both performance and reliability.

An implication of Allan's statement about 'replacement' is that you had better back up your iPad before you send it anywhere (you should be anyway)