options for 500mm?

vjack wrote in post #4631300
If money was no object, I would not be able to resist adding a 500mm f/4L IS to the arsenal for birding, but this is well out of my price range at $5,500. Strangely, the Sigma 500mm f/4.5 APO EX HSM does not seem to be much cheaper, listing for $4,199 at B&H. Of course, a far less expensive way to reach 500mm would be the Sigma 50-500mm (Bigma) or Tamron 200-500. Are there other viable options for reaching 500mm I'm missing?

I agree with everybody's responses, but just wanted to point out that 5500 and 4199 is a pretty big difference in my book, especially when sales tax is included. You're talking 1500 dollar difference. That's nothing to sneeze at.
me

Yes, the 300/2.8 IS route isn't a bad idea. I have one. But, if you are only going to be doing wildbirds I'd say look at other options. Now, if you also do sports, portraits and such, the 300 is a great lens and can do birds as well.

vjack wrote in post #4631300
If money was no object, I would not be able to resist adding a 500mm f/4L IS to the arsenal for birding, but this is well out of my price range at $5,500. Strangely, the Sigma 500mm f/4.5 APO EX HSM does not seem to be much cheaper, listing for $4,199 at B&H. Of course, a far less expensive way to reach 500mm would be the Sigma 50-500mm (Bigma) or Tamron 200-500. Are there other viable options for reaching 500mm I'm missing?

You're saying the above lenses are out of your budget range.....what is your budget for this lens. Also, are your intentions to use it mainly for birds and wildlife mounted on a tripod or are you intending to use it for other things like sports?

Peter

The versatility of the 300 2.8 & t-cons works very well for me. I usually have them with me and even travel (fly) with them. If ALL you shoot is birds, maybe not the best way to go, (although I do shoot a lot of birds.)

I would say slapping TC's on your 100-400 or getting a 400mm F/5.6L and TC (with a non reporting TC you could retain AF) would be the budget way to go

if all i needed was 500mm, i would go for the 400 f5.6L with a 1.4tc without thinking twice. i can tell you right now that my 500 F4 is a 700mm lens about 99% of the time...

When you get to "500" your gonna want to go out farther say to 600 or even 700. where does it end. lol Get the 500 or 600 with a 1.4 and your good to go. No worries about IQ. Just make sure you have a good tripod or monopod for the 600. I handhold my 500 with good results.

vjack wrote in post #4631300
If money was no object, I would not be able to resist adding a 500mm f/4L IS to the arsenal for birding, but this is well out of my price range at $5,500. Strangely, the Sigma 500mm f/4.5 APO EX HSM does not seem to be much cheaper, listing for $4,199 at B&H. Of course, a far less expensive way to reach 500mm would be the Sigma 50-500mm (Bigma) or Tamron 200-500. Are there other viable options for reaching 500mm I'm missing?

Well...other than the money thing, I'd be more concerned about how such a lens would fit into your shooting style. The Canon 500 f/4 is HUGE for lack of a better description. I'm sure I would find it a fun lens to use for a day or two but (for me) it would rapidly lose its amusement value unless I could find an unemployed Sherpa to schlep it around for me. I'd say your 100-400 is still your best option; adding other lenses that overlap that range like the Bigma seems redundant. CyberDyneSystems mentioned a used 500 mm Sigma f/4 as a lower cost possibility; at least if you go that route you could likely sell it for what you paid if it doesn't work out.
Nice Bird gallery BTW.