The more comprehensive kits ($45 Uno, $50 Mega) are for hobbyists and students who wants to get a bit more hands-on with creating! It will include an Arduino Uno or Arduino Mega, and the following items:
Comprehensive kit - $45.00 * Uno
Comprehensive kit - $50.00 * Mega
Basically, the Mega is larger and has a lot more digital and analog pins, you can write larger programs to its memory (Flash), and utilise more run-time memory (SRAM).
The Uno is a great starter board, and its smaller size can be convenient for certain applications.
$48.00 AUD (for each Uno kit)