Yep....I've been through this a BUNCH of times. I work at a dealer, used to sell JD until 2004 (I was there from 1992 through 2016). The old JD LX100 series (LX172/176/178/186/188) were GREAT mowers but the dad gum hood was made out of GLASS. If you breathe on it wrong, it'd shatter-worse when cold. And yep...$750 to replace the upper & lower portions as a set. The green parts store is where I bought the one for my old LX188-which I LOVED (all but the hood....), was $688 complete with harnesses and everything. I had to sell my spare mower to pay for the hood on the JD; and got my money back on the JD after replacing the hood (paid $688 for the hood, mower cost me $100 to purchase, sold it for $1500)-but that mower was CLEAN and low hours. It literally looked almost brand new-even had the original blades and belts.
They still use the same materials to build hoods to this day. I know this because I work closely with another dealer that still sells JD, and they're always telling me that so-and-such driver picked up a customers JD and the hood flipped up or they flipped it up to check something and shattered it. Then the dealer gets to buy another hood for a possibly $100 machine. Yet one more reason I wouldn't own another John Deere. Their customer service got a call from me about 5 years ago because I had done the same thing...picked up a customer's mower, flipped the hood up (carefully since I have experience with them), and as soon as it hit the stops on the hinges (which are also plastic)-it broke, fell to the floor and shattered into a thousand pieces. CSR said they are still manufacturing them basically the same way but with bracing now-which tells me that there was no or very little change made to make them more reliable and/or less expensive.
Now all that said, when I did sell/service them, we had tried everything to repair them and in the end, it didn't matter. Put an hour's worth of work into prepping and welding the cracked hood back together-which came out good, but eventually broke again, maybe not in the same place, but they always broke again...and we (dealer) were responsible a few times to replace the hood "because we broke it in the past". It doesn't take long for a $600+ hood to add up in costs. You'd think a dealer would have enough income to offset it, but sometimes that thought is dead wrong.