sounds HIGH to me, but i have no clue what exactly is involved in lowering YOUR drain. most of them are not that hard to do, but certain situations it could be an all day job.

if it truly is going to cost that much, then i would just do without a GD!

Whatever is involved, that's too much, even if it takes all day. Is this the ordinary bolt-to-the-drain type of GD? Those are usually simple to install, IME. If I were in your position, I'd let him finish without it, take a breath, step back and get some other opinions on what to do.

The problem isn't bolting this to the drain. The problem is that your wall drain is too high. Often, when people get new counters and undermount sinks, their sink is much deeper than the old one. As a result, your drain stub from the wall is still set for your old sink. Adding a GD to the new lower drain makes it even lower! So, you need to run a new drain line from the vertical stack in the wall, which is often mounted several feet away because we all like kitchen windows. I'd live w/o the kitchen disposal, or do most of it yourself.

I'm not a plumber. But you can do most of this yourself--it just takes time. And your plumber will do it all for 110 an hour...

Ditto others. Live without it for a while and consider your options. If it's that kind of job, you can do it any time. From cyber-distance, can't tell if proposal reasonable or not. However, if it cost me that much to have one, I'd do without.

If you have a crawl space, one solution could be to cap the current line as it comes out of the wall and run a new one either through the wall or through the floor of the cabinet. Most prefer through the wall because of the space taken away, but going straight down after the trap is easier. The line can then be tied back in to the waste pipes with less complications under the house.

If the vent pipe will normally be close to the sink. If it is too far away, sinks can be vented with a studor valve instead of using a vent pipe in some places. Then all it would take is running a new line at the appropriate slope to an already connected drain pipe.

Thank you everyone. Problem solved. I was lucky enough to have another plumber in the area give me an estimate and install everything. It took 4 hours and was $950.