Google Apps Script - External API to Sheets

I need a Google Apps Script that reads out the data from this API into a google sheets spreadsheet: [login to view URL] The API is well documented there. The authentication used by the API needs to be send in the HTML header and incl. a nonce which must by dynamic (timebased). This is the data call I need: getGains And this is the data I want in my google spread sheet (for all coins available under the getGains request) [BTC] => Array ( [coin] => BTC [amount] => 1.78089028 [cost_per_unit] => 2291.86172749 [current_price] => 3308.66 [change_percent] => 44.37 [cost] => 4081.55 [current_value] => 5892.36 [unrealized] => 1810.81 [realized] => 173072.97 ) And this is how the data should be put into the sheet coin amount cost_per_unit … BTC 1.78089028 2291.86172749 … … I would need a refresh button to manually call new API data I need an custom menu within my google sheets menu to open the script via a pulldown on any sheet. Should coins/data -arrays be added in the API-Data-List the next run of the script should also add those new coins/data-arrays to the sheet automatically. If coins/data-arrays aren´t available any more from the API they should NOT be deleted from the sheet. Please tell me how much that will cost me overall and how quickly you can code it after I´m giving you a GO. I will give you a test key and secret after we came to an agreement on your proposal.