When I swapped from R4s to R1s, my tractor would no longer fit in the barn - it was too tall by the bubble of the canopy. So I got a 4'x5.5' piece of 1/4" aluminum deck plate, had it bent a couple of times in a big sheet metal brake, and put it on the existing Kubota canopy mounts.
Anyway, I have the original canopy in good shape that I'd gladly sell for $100, but I'm afraid the shipping would cost you both arms and legs. You'd still need the mounts.
So, the aluminum was about $175, the bends were $25 total, and I would imagine you could build the mounts for $30 or $35 - they are a couple of 10 ga sheet metal triangles about 15" per side, a couple of 30" pieces of 1-1/4" sq 10 ga tubing, and 4 rectangular clamps. It all just bolts together - no welding.
Aluminum is 95% reflective in the infrared, so the canopy is probably even cooler than the fiberglass one.