Oh, I have an idea for this lens. Its all dependent on condition in the end.
Going appropriate rate is anywhere between $100 and $300. Most in the $195-235 range. They are so susceptible to haze, and that's the catch in pricing. A truly stunning, real mint example is honestly worth $300 (possibly more, depending on the day). Seriously. That's because the lens is a real performer.
Because most have some level of used condition (i.e., not new in the box) the value tends to be lower. With signs of previous use (love?) and no haze/fungus/separation I'd be above $200, possibly up to $260. Most of these lenses, however, have a hint of haze or enough "cleaning marks" to be of concern. Those could still fetch more than $200, but usually just under. Haze, even a little fungus, separation, and the like will drop that price substantially.
Gerry, you're in OR. Check out Pacific Rim Cameras in Salem. They have a website with all their inventory listed. Prices, and usually photos of the item. They are particularly fond of Canon, from the earliest years to today. They tend to have a few 50/1.8 ltm listed at all times. Keep in mind that they are what I call "retail used" prices. Fair for the most part, but nobody getting a deal. Reflects the PNW market well if you keep that in mind. They have a few right now ranging from $135 to $195. Again, I suggest taking a look. There's a description of the lens condition, a photo or two of it, and the asking price.
http://www.pacificrimcamera.com/
My Canon 50/1.4 came from PRC and I truly couldn't be happier with it.