0% financing is typically a bad deal because if you lock in on the financing you lose your ability to negotiate on the price. When people get all excited about one aspect of the transaction they make a big mistake.
Think of it like 20 k at 0% or 17K at 5%.
Right now Mazda is only offering 0% on 36 months. There is currently a $500 bebate available regardless of who you use for financing.
I have found San Diego to have limited competition so you may want to pick up pricing form a couple of out of town dealerships that are higher volum. Ask to speak with the fleet department
Find Out where they are relative to invoice and then figure the you ahve an addiitonal 500 back of that price becaseu of the rebate available.
Combine that sales price with the finannicing you can get on you own and I will be it will will be a hell of a lot better than simple taking MSRP and the 0% financing.
Good Luck
If you like the Mazda 3 I am surprized you did not take a look at teh Mercury Milan/ Ford Fusion. That is a lot of car for the price. I guess that comes down to what you like but I look at these cars as a fairly competitive deal at the moment.