Definitely contact your local nurseries and contractors -- they love to get their hands on mature specimens. And they also have heavy equipment to move them. A mature agave (3-4') at my local nursery costs $600 and up, depending on the variety.

I watched an episode of a home improvement show where a portion of the reno budget was covered by selling a mature saguaro they had in the yard. A landscaping crew came with a truck and a crane, and took it away.

Any chance you can post a pic? I'd like to see The Beast...

That's what I would do. Taking these things out is not for the faint-hearted. In addition to being nearly lethal due to the spines, they weigh a ton. Since it's free to post on CL, give that a try and see what happens. But make sure whoever says they will remove it seems to know what they are getting themselves into...

I don't know about selling it, but I do know a bit about removing it. It is a messy job and can ruin a saw blade with the slime. Depending on the variety of Agave, you can also get a bad allergic reaction from the slime.... maybe an actual burn from certain ones.

IMHO: If you do decide to remove it let the experts do it. They know what to do, how to do it safely, and have the right equipment.

Problem with agaves is that if this particular one is monocarpic, the older it is the shorter its lifespan. And if you stress the bejesus out of it by moving it, it might just respond with a flower stalk and then it's all over.

Good point, Sarah! My agaves are still in their teenage years, I keep forgetting they don't live forever...

I have a friend who had a huge A. americana (is there any other kind?) and after flowering she was at wit's end trying to figure out how to get it out. Somehow - I don't remember how - she got a call from a guy who makes surfboards and he uses Agave flower stalks as his preferred material. So he came and took it out no charge. But he fell off the stalk while he was working on it and while he was ok, he was pretty scratched up!