[Ethereum] API or code to find the current price of a ERC20 compliant token listed on Etherscan

Etherscan's FAQ page answers your first question in the "Token Tracker Listings" section. Here is what it says:

Any compatible ERC20 tokens on the Ethereum blockchain can be publicly and transparently tracked via https://etherscan.io/token-search

In addition to the above ERC20 token tracker, we also have a selected list of tokens at https://etherscan.io/tokens. The decision to list these tokens here are based on the following criteria, but not limited to :

• Token Popularity and Demand (important)
• Supported by a large exchange (i.e Poloniex, Kraken, Coinbase)
• Has a unique proposition/utility
• Visible website, about us, team page, company mailing address, official support channels like reddit, twitter, slack, facebook.
• Fully ERC20 compliant (https://github.com/ethereum/EIPs/issues/20)
• Is NOT a ponzi, pyramid, mlm or other similiar schemes

You may request for a token to be added on the https://etherscan.io/tokens page by filling up the following form https://docs.google.com/forms/d/e/1FAIpQLSe9t2VBwje7zO_xMKT3bO92H8nrzsQJCu2KeFU3PLgAjRONLA/viewform , however the ultimate decision will be at our own discretion.

Here's json result from your api call:

{
    jsonrpc: "2.0",
    id: 1,
    result: {
        blockHash: "0x8fe66b0c15a1c1155338bb5628db55f05cfe72d1194931134b4721cd07e9eda7",
        blockNumber: "0x416850",
        from: "0x167a9333bf582556f35bd4d16a7e80e191aa6476",
        gas: "0x13880",
        gasPrice: "0x4e3b29200",
        hash: "0x03430ecdf52d37a8d3645fa9b19c072ec367edbd0d4eba3cc1c7f7c5e7dcc7d2",
        input: "0xa9059cbb0000000000000000000000007a2641bb2fb31ccd33ba5488c886c3bc4714ec6b000000000000000000000000000000000000000000000054ca7578dcf8bb7aa0",
        nonce: "0x15a82",
        to: "0x9a642d6b3368ddc662ca244badf32cda716005bc",
        transactionIndex: "0x2a",
        value: "0x0",
        v: "0x25",
        r: "0x790a06d5773006ecbc719354d966d100470e6267a68d3446ca0ebfd8df4452b5",
        s: "0x4e58eb2997a3c8add1386a47a71ac5bb915a2a53343883ea1ea4d8e69a6be486"
    }
}

Please take care of the input field:

• First 4 bytes is method hash:

  a9059cbb
  

• Next 32 bytes is target address:

  0000000000000000000000007a2641bb2fb31ccd33ba5488c886c3bc4714ec6b
  

• Last 32 bytes is value of ERC20 tokens transferred:

  000000000000000000000000000000000000000000000054ca7578dcf8bb7aa0
  

0x54ca7578dcf8bb7aa0 = 1.5641152016500001e+21