I've seen used examples of that grinder listed at anywhere from $1,000 to $1,800. That doesn't say they sold at those prices, but they were listed, anyway.
What could you, realistically, get for it off of, say, Craigslist? Depends on your area. I gave $50 for my Queen City, and I was the only one that even so much as called the seller on it. At the auction the college had a few years ago, they sold two more- I think both Baldors, one was a 5HP (!) and the other a 7.5HP(!!) Both went for the starting bid of $50, and I clearly recall one guy saying something like "Oh, what the hell..." on one of them.
Could we turn around and sell them? I'm not sure. Locally (sort of) there was a seller up in Anchorage trying to unload a 10" 1.5HP Baldor, 3-phase, with starter and original stand, for $400. He kept relisting it for months, eventually throwing in an old 8" Rockwell to sweeten the pot.
He may have finally sold it, as I haven't seen it listed in a while, or he may have given up, I don't know.
But the lesson there is that even a more home-shop-friendly size machine, in very good shape, with extras, wasn't exactly snatched right up, if it sold at all. 3-phase still puts off a lot of people; either they don't know that converters are available, or don't want to hassle with starting a rotary in order to use it, or don't want to put a $250 VFD on a $50 machine.
What you might do is put it up for sale at, say, $400 or best offer. Put a link in the ad (if it's Craigslist) to some place like Automation Direct's VFDs, or American Rotary's DIY rotophase converters.
If it hasn't sold in a month or so, drop the price and try again. Best I can suggest at the moment.