I'd say historically 30% off MSRP with a rational dealer prep was a great price. I have no idea today with this covid thing. My fear is the balance favors the manufacturer/dealer due to high demand and lower supply. I think you have to be a savvy shopper and target in-stock boats at the right time (in the NE I'd say Nov-Mar) when a dealer wants to move so they don't get stuck with a non current boat. You may have to settle for not the exact boat if you want a good deal.
When settled on boat price, then look at other things - negotiate to provide your own electronics and have the dealer install at a fixed price, negotiate bottom paint, full tank of fuel (should be there anyway) first year services if you can - including first year winterization and storage, look for things that would cost you but not the dealer so much, negotiate other gear like safety or fishing. One tip I was given was to get a prop wrench tossed in at the very end as the cherry on top.