I did this using only JavaScript to make it very lightweight and simple... Integrating it into your current page is not an issue at all. It cam be styled (font, font sizes, colors, alignment, etc...) any way you want. It will currently inherit the css you currently use and for anything specific you want, I can add some inline css very quickly..
I am using the coinmarketcap APi to get the pricing data, so it is slightly different from ontcalc.com's pricing. the difference is only a couple of cents, but the calculations on the ONG generated, ROI and time-frames is all correct and checked against ontcalc to be sure...
Here it is, live on my server....
ONT/ONG ROI CalculatorInstalling onto your site should take no more than a few minutes
You never mentioned the price you were willing to pay, but I trust it will be fair. My Bitcoin wallet address is 1PuD4f3q8ji9djAqNaGkwyEYZrmqH1Ui6Q