Randy,
You'd better sit down. Oh, yeah. You already are.
I was investigating a stair lift back in December '08 as a way to keep using my master bedroom upstairs. We ended up remodeling the downstairs instead and I use a $3000 platform lift to carry me 30 inches vertically. It's a MAC's Lift PL-50. Got it on craigslist for $1500.
First of all, don't get a chair lift. These are the things where a small chair folds out of the wall. These things are fine for some people, but not for ALS. Our progression gets to the point where our trunk muscles don't allow us to sit on the chair safely. These are nice and cheap though, compared to the stair lift.
A stair lift allows you to roll your wheelchair onto a fold-out platform, and the whole thing glides up and down the staircase. This is what you asked about, and probably what you need.
My stair lift research was mostly centered around McKinley Elevator. You can find them online easily. In my case, the finished solution was in the $40k ballpark. I have more detailed notes here somewhere. The price will vary greatly depending on your home's architecture. Is the stairway straight or curved? Is there a landing zone at the bottom of the stairway with plenty of clearance? What is the strength of the wall next to the stairway? Usually the wall needs reinforcing. Is there sufficient power (220V) in the wall (probably not)?
Take some measurements and give them a call. I hope you can find another alternative.
-Tom