If you are after new one's i have seen them cheaper than that on Ebay,you could always have
a look for some used one's.
But you could always repair the seal and do the
black eyes mod at the same time. :L
have you taken the light out to see if one of the bulb covers has come loose or fallen off the back,this could be letting in condensation.
(The lenses should be plastic and not glass),failing that you could just run a bead of sealant around the edge,where the lense meets the main body of the light.
If you keep looking on ebay you can pick them up from Â£10 plus around Â£10 for the postage.
I've taken the lenses off mine a few times now for various reasons and have been lucky so far,and thats with no sealant just heating up the old sealant with a hair dryer,and squeezing the joint together.