business case is prety simple, i mean the UC (link/text hook).
But an add-on for every wb? too many versions. You will have to specify what versions you need.
$200 for each of big 4: FF, IE, Safari and Chrome. 800 in sum.
FF and IE could be the fist milestone. IE 6,7,8 and FF 3.6, 4.0 I guess.