Convert gas price in GWEI to USD or ETH

There is no minimum for gas price

You can set a transaction with 10wei as gas price if you want.

The problem is most miners won't include transactions below it. You can see here http://ethgasstation.info/ the minimun gwei each miners pool ask for. It seems right now the minimun is 1gwei and it will take 1.5 minutes.

However with tools like MyEtherWallet or Metamask the minimun is indeed 2gwei because actually it is "the cheapest" miners accept.

But in the future we might see this reduced again but for this more miners will have to accept transactions below it.

If you want to set manually your gas price I advice you to use a client like geth

eth.sendTransaction({
 from: '0x036a03fc47084741f83938296a1c8ef67f6e34fa',
 to: '0xa8ade7feab1ece71446bed25fa0cf6745c19c3d5', 
 value: web3.toWei(1, "ether"),
 gas: 100000,
 gasPrice: /* gasPrice in wei */ 
})

Remember one gwei is equal to 1billion wei

On your link you have the contract address, which is 0x169e633a2d1e6c10dd91238ba11c4a708dfef37c

And you have this specific function that you can call to get the current gwei:

function latestRoundData()
    public
    view
    virtual
    override
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );

It will returns something like this:

You can call this function from your smart contract if needed, if you want the USD price, you can do the same process by multiplying ETH/USD price by GWEI, ETH/USD