Hi Paul, nice to hear that there is another junior racer coming onto the scene. My son has been catching a few local (Roseneath/Norwood) races for the past couple years and this winter we are building a new mowchine for him, and hopefully me too! You can follow our build in the appropriate section of this board, although we have not posted pics for a while now.
I didn't have any success finding a RAGB until I got onto ebay. They come up regularly and I have picked up a couple really nice ones for under $100/ea including shipping.
If you are in a bind, I have an extra one here that I could let go. Cheers