hi
you should be able to easily drive two Arduino's stepper motors with one stepper Arduino...
With an L298, you would use 4 pins for the motor windings, and 2 pins for the enable. Two motors per Arduino. There's a diagram for connecting the L298 to a stepper motor in its datasheet.
Then, if you just want the Arduinos to passively receive control codes and activate the motors, you can hang several arduinos off of one RX line, and have them all watching for the appropriate control signals. If you use Paul Badger's barebones Arduino, or the NKC Arduino, you can build each dual motor controller for about $20-25 in parts.
D