I went and returned my Cateye EL500 today as it didn't seem bright enough for a primary headlight, and I was going to get the 510 which looked smaller. I had been in last week and gotten the EL500 for $34.83 on clearance, and saw the 510 at $19.83. Both of these have been replaced with newer "50% brighter" models.
After returning it today, I went to the lights and found that both were sold out, but there were signs about "50% off extreme clearance prices (that end in .83)". Not finding the 510, but thinking these lights (which were now both cleaned out) might be included, I went back to the return counter, retrieved my return and went back up front and checked out - for 17.42+tax.
I expect there are few stores with stock, but it's a screaming deal if you can find it. I guess I'll use my 500 as the backup to the Alias I just bought, but was looking for a smaller light for that function. At that price, I can't complain.