The Tesla Model 3 price starts at $35,000 before any tax rebates or incentives. To calculate how much your Model 3 might cost, please see our cost google spreadsheet. At least at this time, it is not possible to lease a Model 3.
Tesla's website does a great job summarizing the tax incentives. In the US right now, current Tesla purchases are eligible for a $7,500 federal income tax credit, and some individual states offer their own benefits. Colorado residents are eligible for an additional $5,000 tax credit, lucky them!
The question remains, however, exactly what incentives will be around by the time customers can actually purchase their Model 3. It doesn't matter when you order the car, any possible tax incentives only come into affect once the car is put into service. Assuming the tax credit for electric cars remains as it is now, the federal $7,500 credit begins a phase out once Tesla sells 200,000 cars to U.S. customers. It is very important to understand that the credit is not all or nothing, there is a phase out that once Tesla crosses that 200,000 mark, there will still be some credit available for the following year of sales.
The phase-out period stretches over one year, beginning in the second calendar quarter after the quarter in which the manufacturer hits the 200,000 vehicle US sales mark. From there, all qualifying vehicles sold by the manufacturer are eligible for 50% of their specified credit for the first two quarters and 25% of the credit for the next two quarters (thanks, dhanson865).
In July 2017, dhanson865 over at TeslaMotorsClub.com did a great job breaking down his best guess on the federal tax incentive phase out schedule.
According to electrek, In January 2017, Tesla crossed 100,000 cars to US customers (out of the 200,000 incentives available). It's possible Tesla could tip over 200,000 cars sold in 1st quarter 2018 instead of 2nd quarter (if Model 3 ramps up quickly), so it's possible the phase out could begin a quarter earlier.
We now know that the first Model 3's sold will only be the larger battery with the premium package, followed by production of standard battery cars, and then finally the AWD model. I waited in line outside Philadelphia and have estimates of January-March 2018 for the standard battery, and July-Sept 2018 for AWD (delivery dates likely sooner in Cali). It's likely if you want AWD, you'll still get some rebate available to you, but it won't be the full $7,500.
Finally, not a tax incentive, but some electric companies may offer additional incentives for customers that have an electric vehicle, so that's another bonus that may be worth looking into. For example, our local provider PECO will give you $50 per car for letting them know you have an electric car.