Send text according to an ultrasonic measurement, on battery.

I have this big bucket where I would like to install an arduino on the top of the bucket where it would calculate the % of the bucket being filled up with water. Then, every day at night the arduino will send a text message (via SIM card) to the server where it would collect data for that bucket.

As far as a beginner point of view, I can understand that I will need:

an Arduino Board
PING))) Ultrasonic Distance Sensor
Battery pack that would allow to run the board for a year?
and the Arduino GSM Shield (integrated antenna) OR the GSM/GPRS Module M10?

My question is:
What arduino board do I need for my setup?
How long will 2 large or 4 AA batteries lasts for receiving a value from the ultrasonic sensor once a day and sending that value to a server? The point of the instrument is to be as small as possible.

Thank you