Don't buy new. There would be plenty of impulsive photographers like mackguyver and me who used it for five minutes then pushed it straight out onto eBay/Craigslist/Gumtree. You should get a pristine one for under $100.
I'm still trying to decide what to do with mine, but that's good advice. I think a lot of us got one for a good price, but haven't found a use for it. My main issues with it are the AF speed (I'm so
spoiled by USM), the f/2.8 aperture doesn't get me anything over my zooms, and I find the EOS M + EF-M 22mm much more convenient. I don't love the focus by wire, either. I hate it on my 85 f/1.2 II and EF-M lenses already, but they offer so much in exchange that I don't mind the trade off for them. On the 40, I just find it annoying.
It's a fine lens, and it would be great for landscapes and relatively slow moving subjects, but I don't seem to be able to find much use for it other than as a small backup lens. Of course, I might was well carry the M + 22 combo so I have a backup body and lens.
Maybe it will find a place in my kit, but it has spent a lot of time on my shelf so far...and is in imminent danger of going up for sale.