Personally, I think the only way to get one by EOY if you don't already have an order in is to take from available stock in your area. Many of us have been waiting many weeks since ordering (I'm at 8 weeks today).
What build are you waiting for, for 8 weeks?
I suspect that if OP wants one by the end of the year, OP needs to not only willing to take from available stock, but also know that, for Model 3, "Available stock" seems to be:
1. All wheel Drive model (NOT rear wheel drive)
2. Long range model, or Performance model, (NOT Medium range model)
3. Be willing to get black seats (although white seats seem to be available, especially in the performance model.
Just from talking to the manager at my local tesla store and reading here, people in southern california have been able to take virtually immediate (less than 1 week) order of cars in various colors meeting the specs above (All wheel drive, Long range or performance).
People still waiting seem to be waiting for the mid range model, or rear wheel drive. Personally, I did not need all wheel drive because I am in southern cali and dont need 4 wheel drive for weather. I DID want the performance model, however and thats the only way it comes so /shrug.
I "placed an order" on 11/27 and they matched me with a car the next day. I took delivery on 12/04. I was NOT a reservation holder, nor did I have a previous telsa EV (although I do have solar city / tesla solar, so was able to self refer myself... but I did not get any impression that had anything at all to do with the speed with which I got the car.
OP if you dont plan on an all wheel drive long range or performance model, its my opinion that you can basically kiss goodbye any hope of getting one before the end of this year. If you DO, and are willing to take one of the already manufactured cars made in november or december (tesla does not have cars sitting around for months, they dont have a place to store said cars). then I am fairly sure you could get one by then, even delivered to arizona however that has to happen. If delivered by dec 31st you can claim the tax credit on this years taxes (if applicable to your tax situation). If not delivered this year, you would be claiming on NEXT years (as in 2019 taxes filed in 2020) and also lose half the rebate.
Its "better" to find outside financing, if by "better" you mean "cheaper". Unlike other major car dealers (BMW, Audi, mercedes, Toyota), Tesla does NOT have a "captive" finance arm. By "captive finance arm" I mean a financial institution they have that just performs loans and leases for their vehicles. An example of this is "Toyota Motor Credit" or "BMW Financial Services". Tesla just has agreements with some bank (not sure which, and I think its a couple).
So, Unlike say BMW, which will many times offer lower rates than readily available to move cars (and is the only way to lease their cars, basically), Financing from tesla is just financing from whatever financial institution they use. Most times it seems a credit union has better rates, but you may have to jump through some hoops to join it, based on what they require. In my specific case, I went with my own financial institution which is navy federal credit union, which offered 3.59 over 72 months (which is a decent rate for that term right now.) Some were cheaper per the referenced spreadsheet above, but I already bank with Navy Fed, and the application took me about 5 minutes online and a few clicks, and paperwork delivered to my local branch.
As for the 2500 deposit, the best way to think of it in terms of how it works is like a "diagnostic fee" on your car when you take it to the shop for service. When you take your car to the shop for service, and the dealer or mechanic tells you "I charge $199 for a diagnostic fee, and that gets applied to any work that needs to be performed", What they are saying is:
"we will apply the diagnostic fee to any work you decide to do because of the results of the diagnostic fee, but if you decide to do NO work after the diagnostic process has been performed, we have earned that diagnostic fee and will not be returning it"
Tesla's deposit works the same way. They say its not a deposit. If you pay the $2500 deposit teslas contracts clearly state that they feel they have "earned" that money once they have gone through the process of matching you with a car and getting you a VIN number, however if you complete the purchase the money is taken off the balance due on the car.
So, not "deposit" but functions like one because it gets deducted from the price of the car once you complete the purchase. If you DONT complete the purchase and they have already matched you with a VIN number and attempted to schedule delivery, they dont have to return it. In fact their contract clearly states this, however people have reported that they have returned it to some in that circumstance. I think its important to know the difference, however. Gets deducted from the price of the car, but does not have to be returned if you change your mind AND they have already matched you to a car.
If they havent matched you to a car / vin, then can be returned with no issues.
Given this is the end of the year, and if you were willing to take a model like I said above, you would likely get matched with a car almost immediately (again, as long as you were not wanting a medium range, or rear wheel drive only car, or set on having one only with a white interior instead of black in the Long range or performance models).
Hope this helps.