I'm not a finance expert, which is one reason I pay cash, but yes I think after 6 months it'll be moot. You have an collateral problem, being upside down on the M3. Who knows, once you've made 6 months of payments, go back to the CU and ask them to run the numbers. If it saves you money to refi at that point, do it.
I wish I was in a position to pay with cash!
I calculated the true loan cost and these are the numbers I came up with:
Mazda financing: 22900 @ 4.99% for 72 months = 26,546.17
CU financing: 22900 @ 2.24% (at best) for 72 months = 24,494.68
The difference is 2,051.49
I mean, two grand is two grand, but it's not such a huge difference that I'll lose sleep over it if I can't refi.