That's easily a $900 - $1000 worth of signal cannon. I'm surprised that you're selling it so inexpensively. If times weren't tough with me, I would buy it in a heartbeat.
Your machining, welding, and assembly work are amazing.
That guy, Rick, from Pawn Stars (Las Vegas) is a sucker for cannons. Bet you could get him to pay $750 for it.