Premium aquatics has dual 250W PFO ballasts on clearance for about $160 each (not electronic, though) - I was looking at downgrading myself, as my new setup came with 3 400 watters. As I've dropped a lot of coin already, I settled with just using 2 of the 400s for now, and have been pleasantly surprised by the penetration and light spread of the 10Ks I just installed. (20s are too blue for me)
Good luck, they do burn up the energy bill!!