Asking prices on Ebay vary from $25 to $1000 for the same item sometimes. Especially "BUY IT NOW" offers: these are almost always unrealistic prices.
However, there is one auction for this lens (with issues) with no price limit, worth following to get a more realistic estimation. See:
You can also check the SOLD items, see:
At quick glance $300 seems a nice price for a seller, but with patience a lot cheaper is possible?