Old Total supply of Polkadot is 10,000,000 New Total Supply of Polkadot is 1,000,000,000 [1 Billion], Now question comes what is the circulating supply of Polkadot.
Polkadot give option of staking and there will a lots of dots in stake. So assuming the real circulating supply will be around 500,000,000
Polkadot have sold 50% of Token in Auction and maximum users have not sold there stake and they have not planned to sale.
So you can consider 20-25% which is 300,000,000 will be the circulating supply of DOT token and it will be among top 20 token in current system and price will jump to 5-10$ very soon.
According to Polkadot Scan around 400,000,000 new dots is in Stake so according to this circulating supply will be very low
Also read- How to Create Wallet in POLKADOT