I picked up a f/2.8 non-is version a couple of weeks back from Craigslist for $350. Owner even had the B&H receipt from about 1998. It had set in its box most of the time and not used at all since 2005.
I had one a few years back as well as several mk I IS versions and two of the MK II vesions. That old non-IS lens is very sharp, not as good as the MK II version, but noticibly better than the MK I IS version.
However, since you want to use it for indoor weddings, and likely handheld, you will need flash or a unusually steady hand.
Outside, I crank up the shutter speed so its no issue. I was using it today, and forgot that it was non-IS. I held the shutter button halfway down and waited for things to stabilize. They did not, so I looked to make sure IS was turned on, and then realized which lens I was using. I then cranked the shutter speed up and the images were sharp.
I'll likely sell it and get another MK II IS version. Now that I have a 5D MK III, I'm not as concerned about higher ISO settings in low light. Usinf f/2.8 in low light with my 5D MK II was marginal, but another stop would work out fine.
I might also look at the Sigma 50-150mm OS, but I am not a Sigma fan to say the least, so it would have to be pretty special to convince me. I do like the focal range though, dropping to 50mm would be nice. It might even be a walk around lens.