Hi marty: way less than 3Gs sounds like my price range...
I just missed a 36 ft ex-house trailer (park model, superstructure stripped off, just the frame), with tandem axle & electric brakes, for $800! I figured a cradle on that, cut some bits off the back, and I'd be good to go. A friend of the present (now previous) owner bought it.
So it's doable for less than $2000 buying a new (cough, hack) cradle, and probably closer to $1000 if everything is used and just needs welding, or bolting together. I can paint.
@sailingdog - I didn't observe in the photos the horizontal bar running side-to-side across the supports at the front and back. Thanks for spotting this! I think this bar could be replaced at the back supports with a bolted bar, to be removed while launching. Additional support could be provided with sideways diagonal bars like the fore and aft bars between the supports and the trailer bed. Look at a Jowi cradle, there's adequate room to slide the keel out backwards between the supports.
Does anyone know where to find abandoned or even used Jowi cradles?