Find out what your rate is at the same loan term that you’d finance with either dealer.
If dealer A has it on the lot, and I were in your situation, id start with an offer lower than 10-11k below their MSRP.
If you don’t want to haggle, you should start with a price around 46k before accessories and before TTL and remind the salesperson you have financing but would be happy to use theirs. I would do this over text or phone but not email so they know you are serious and not shopping them for the lowest price.
If you do want to haggle, same as above but don’t give the opening offer - make them give the first price. Do remind them you have financing but would be happy to use theirs if the rate is competitive. The key here is to see where you can start negotiation from. If they understand you are serious they will start with a serious price. But this may take a bit of back and forth.
Being open to their financing (not the 0%, just financing with the dealer) will open up a world of extra discount possibilities.
What you feel comfortable paying is up to you and your own situation, but I would be dead to rights shocked is if you end up getting less than 10k before accessories and TTL. 11-15k should be possible, that will all depend on what the dealers motivations are to close their quarter and calendar year books.