According to preliminary estimates, the project should be completed by 2020 at a cost of about RUB 40 bn.
This (first) option is better because it is more natural and reflects a certain usage of the indefinite pronoun: talking about, um, indefinite, or tentative values.
When our car is damaged, we call our insurance company or a car repair shop for an estimate (an estimated cost to repair the car). I don't think anyone would initially call and ask for the estimate. Once Joe's Body Shop gives you an estimate of $600, you can call back and squabble about the estimate. Or you can compare the estimate of Joe's to the estimate from Dan's Garage.
Similarly, when we talk about other tentative values:
Freezo is trading at a price of $25/share.
Flight 7 has an arrival time of 10:30.
We have a high bid of a dollar twenty. Do I hear a dollar thirty?
It is not until the auction is over, the stock market closes, and the plane lands that we talk about the value. I stated that tongue in cheek. Of course, you can also refer to the current estimate, the current bid, the current arrival time, etc., but current values do not change. It is currently 10:00. In one minute the current time will be 10:01.
What's the arrival time for Flight 7? Well, 10:30 is the current arrival time, but who knows when it will actually arrive?
What's the prelimnary estimate of the project? Well, about RUB 40 bn is the current estimate, but who knows how much the estimate will increase over time?