my bunny has done 2 week long roadtrips (cross country moves) three times now and has been fine each time.
i purchased a large cat carrier at a yardsale for $10 and use that for him. perhaps you could find one as well if you wanted to go yardsaling, or even look into local buy and sale facebook groups if you’re worried about the cost. you might find a good deal (just be sure to give it a good wash first!).
i covered the bottom with wood shaving (he’s litter trained but will go in shavings too), put a handful of hay in and some pellets, and hooked up a water bottle which id put fresh water in during stops. he also had greens available to eat at his regular feeding times. and i put some things in his carrier for him to chew (to give him something to do), and one of his fav stuffies (something to comfort him).
the worst trip was in the summer because of the heat, so id advise keeping an eye on bun to make sure he isn’t panting or looking ill. if he’s looking hot wet him with a bit of water (i put it on the back of bun’s ears), and see if you can’t get them to drink some water.
and of course on stops id let him out to roam the vehicle or hold him.
also, i keep out anything my bun might need in emergency, like baby oval or pedialyte, droppers to give it to him, etc. like a bunny care bag lol.