That's there over inflated price now, five years ago they were $50 - $75. If you keep watch you may get lucky took me about six years to find one in a lot on eBay wasn't listed but pictured with other items I got the lot for under $30. . Most 5C collet accessories are as high brand new. Like the taper attachments. They all think steel is gold.
Keep in mind that the spindle adapter is in no way a South Bend only part. It is a Morse taper O.D. and a 5C collet bore I.D. Grizzly sells a Chinese one for a little over $100. I have one, and it had .0006" runout as received, my spindle is within .0001". Others have reported the same type of inaccuracy. I have partially ground mine into true with my tool post grinder, but need to get a different wheel for it to finish the job in under a week's work...
The pictures of the one on eBay do not show the tapers well at all, might be all rusty, galled and scratched. If you want it, I suggest you get some better pics and place a low bid on it, or go to Modesto and look at it.
Gary Aragon has quite a few of those adapters at his store in San Leandro, at much better asking prices than the one on eBay. http://www.garysaragon.com/
Edit: Also, the L00 spindle has nothing to do with what machines the adapter fits.