I'm starting my UDS build this weekend. I figured it was important to get the right drum (no red liner, no weirdness), so I went ahead and got a new, unlined 55 gallon drum (open head, bolted) from the Cary Company in Addison, IL. I live close, so I was able to swing by a few hours ago and pick it up from the freight dock, but for $65 ($55 refurbished unlined) also available.
They deliver and ship, but if you're in the Chicago area (and near Addison, IL -- about 25 miles west of Chicago) I highly recommend this place to get a new or refurbished drum. Great folks to deal with -- and once they knew what I was using it for, they made it a point to double-check to make sure it wasn't lined, undented, and shiny and new. Definitely worth the $$$ -- especially now I concentrate on the build and not scraping or burning any liners.
(No affiliation with the company -- just happy they took the time to make sure I got exactly what I was looking for.)