Or, go custom, I know that you can get 25 blue (super bright/12.000 mcd) LEDs + 25 resistors of your choice for under $4.50.
That's not only so much cheaper, but you can calculate the voltage/resistors you need. (EDIT: don't mean to bash you, but prefabricated stuff is overrated and expensive)
Example:
4 rechargeable AA batteries = 1.2V * 4 = 4.8V
1 blue LED with forward voltage of 3.2V @ 20 mA
Resistor = (4.8V - 3.2V) / 0.02 A = 80 ohms, nearest resistor is 82 ohms