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.
In January 2018, Troy over at TeslaMotorsClub.com did a great job breaking down his best guess on the federal tax incentive phase out schedule. It seems very likely that the phase out will begin in Q2 of 2018, meaning the full rebate is available for all deliveries before September 30th, 2018.
We now know that the first Model 3's sold will only be the larger battery with the premium package, followed by the AWD model (long range only to start probably). Finally, production of standard battery cars begins in "late 2018." I waited in line outside Philadelphia (non owner) and have estimates of "late" 2018 for the standard battery and AWD (delivery dates likely sooner in Cali). It's likely if you want the standard size battery, and/or AWD, especially on the east coast, you'll still get some rebate available to you, but it won't be the full $7,500.
There are some Canadian non owners with mid 2018 delivery estimates for the first run production of the car and AWD. Back in April of 2016 Elon tweeted about timing the 200,000th US car to maximize the rebate for as many US customers as possible, but the reality is that every model 3 coming off the line right now (as of the 2017 Q4 earnings call) is not profitable. They need to focus on delivering the most expensive profit heavy cars now and this is most easily done in US and Canada. While it's possible that Tesla could divert sales to Canada to push the incentive another quarter, I am not going to count on it for the standard range model.
Another incentive is available if you installed your home charger in 2017 (this credit existed in 2016 but was extended to cover 2017 installs in the February 2018 2 year budget deal). Here is the text of the bill mentioning the date change. IRS form 8911 is the form you'd need to fill out the claim the benefit, however as of February 11th, 2018, it hasn't been updated for 2017 tax year (I assume that will be done soon). Some members of the Model S forum have claimed the NEMA 1450 in the past (discussion here).
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.