Tallman, I'm not experienced enough with RVs to have a definitive idea for you, but I do want to express my sympathy. Ouch!!! That's gotta hurt to be whacked with that kind of repair bill right away.
And now for a little uneducated speculation...If it happened to me, I'd try to find a place that works with Plexiglass (plastic) and see what they would charge to fabricate and install one (perhaps a double pane) to your RV's window. They make some of that stuff very thick and strong. I find it hard to believe there isn't somebody who'd be happy to do it for a good deal less than a thousand dollars. Hey, I'd even go to a house window manufacturer and see how much they charge to fabricate a special shape (unbreakable) window and install it in such a way that it would stand up to a vehicles vibrations. Also, is it possible to just "patch/repair" or stabilize the crack without replacing the window? But, of course, those ideas are not based on experience, so they may be unworkable.
Whatever you do with it, again, you have my sympathy...and may this be the last thing that breaks on that RV for a very long time.
GP