I ordered the clutch disk from the local Ford dealer and thought $175.00 was high. I had a spare input shaft, so I never asked the price for one. A local used parts place had a few of them, and they go about 1/2 dealer price, down for less than pefect condition. The planetary gears I bought there were in excellent shape, and since I seached through the drum of oil & parts, I paid even less.
I have considered the following, as I figure if I wear out another input shaft, I will have more trouble finding a usable one years from now: If the rest of the shaft is good, grind off the bad splines and build up with new metal by welding. Heat treat to relieve stress. Have new splines cut. Ideally, do this to both hub and disk, using modern spline design that is stronger.
I did this for the swing pivot on my IH 3800 backhoe. It cost $500.00 for the (inner and outer together) spline cutting at a local machine shop. That was roughly 3" diameter.
I don't know the "technical names" of the types of splines, but the original on my input shaft and the backhoe pivot were the type that are "V" shaped. The new ones are square shaped, like ACME screw threads. The new splines on the backhoe are not showing signs of wear.