This module will do it for $20: https://www.adafruit.com/product/1535If you only need 12 keys in your keyboard it doesn't even need an Arduino.
thanks, I think no way to send string to ipad with my arduino like a bluetooth keyboard emulation. Only can send by serial port emulation
Here is a project to emulate a keyboard by changing the firmware on a $3 bluetooth module:http://www.instructables.com/id/3-Bluetooth-HID-Module-HC05-With-RN42-Firmware/What makes you think that none of the proposed solutions will work?
Looks like the best bet is to gut an existing iPad keyboard.