the hairline cracks are a worry, are you sure they are cracks and not casting marks? if the grooves are not too bad you can file them out/down carefully and get some more life out of the basket. uncommon for a 500 to have them i would think as it is usually the way with 125's and 250's (fanning the clutch ) yours may have done a lot of work maybe.
aftermarket baskets are available (Hinson is another brand) but pricey.
do you have a pic to post of the basket?
OEM price would at a guess be $600-700.