The second group of browsers are called Legacy Browsers: any browser which is isolated with no automatic upgrade path. This includes IE 8, 7, 6 as well as any legacy version of any other browser that didn't stay on the latest version. If you don't ask/pay for legacy support then I will design it using modern best practices and it will likely work well down to IE9.
For legacy support, I will support whatever browsers you wish at the normal hourly rate. If IE6 support is dear to you, and worth the cost I will happily dust off the ten-year-old techniques and give you the support you desire.
Keep in mind that IE8 doesn't include support for CSS @media queries, so most forms of responsive page layout will be impossible without the use of a polyfill! I think due to this, many sites that think they support IE8 don't actually render very well.
(Because it's weird to me how many sites serving mostly text and images fail so hard)
Unfortunately we have a number of clients using our product (particularly government) which still expect it to be supported :(
It still makes us around € 30K per month, and it makes sense, for now.