There is a point that you are paying for professional services, and decide monetarily whether the LA would be worth it for you....
BUT...the decision is so much more about money. I had one woman say that it was wrong to call the LA a "TOY", but really it is! You can have a lot of fun and relaxing hours quilting on a LA machine, or you can be a slave to it and make it a business or be forced to justify every penny you spent on it. It's all up to you, and no one else can tell you ahead of time whether it would be a foolish choice or not. When I was researching my LA, I ran into a bunch of people who bought theirs and then didn't enjoy it or use it as much as they thought they would, and thus were selling theirs used. Not everyone ends up liking the quilting part- some end up liking piecing and top making more. I bought mine and am making a go out of a business with it.
There is such a range of LAs from the sit down models with a smaller footprint and a small throat space to the take-up-my-entire basement models. I have a HQ18 Avante, and have my frame set up for 12 feet, but that's toward the upper extreme (the machines can go up to 26 inches, but in reality the frame for those would take up just another foot or so in space compared to mine.)
Prices- a few thousand to $30,000. Join a yahoo group for each of the brands you are considering, and ask people about their machines. You really need to do a lot of research to find out the options, price ranges and limitations before jumping in and buying one, just to insure that you will be happy with your end choice.
Some people just take a regular sewing machine and then buy a frame/carriage set up to move the machine around- it doesn't produce as good of results as the newer machines with stitch regulators for quilting, but the price point is a lot different. The stitch regulators and new machines just glide, and can be really easy to learn on. My Avante is a dream to play with- I've found it super easy, if you get the tension right, which is a process to learn.
Best of wishes.