Yes, I don't have windows, so debugging IE is a bit painful. If there is demand, I would do it of course.
You can add #y=gb to the url, it will change capacity/price to price.
I just brute force the positions. In the first iteration, I go through all empty cells and choose the best. For all items. Then I search for items that can be swapped.
I'd be a +1 for IE 11 (disclaimer, I work at Microsoft on the IE developer tools but use IE at home). Regarding testing in IE, have you seen the http://www.modern.ie website? There are Windows VMs there you can download for free for any host OS that have all the different versions of IE.
how would things look if you plotted just capacity on the y axis instead of capacity/price?
what algorithm do you use to make the points form a grid in the dense areas?