Janome has an 11" machine - the Horizon. It's a sit down. I am not sure how much they go for but that one would have feed dogs. I know it isn't what you were looking for though... it is a smaller necked machine.
I have a Bailey 15" machine on a frame. I do not enjoy frame quilting as much as I hoped I would but then I haven't really pushed myself far with it. I will make a point to really get in to it this summer... maybe I can designate the boys' reading time as my Bailey time... maybe it will grow on me.
It is a great workhorse of a machine. It does not have feed dogs so it is free motion only.
You CAN stretch your own machine. There is a tutorial online to do so. I would suggest getting a cheap machine from a second hand store to do it on though just in case
There is a pdf in the homequiltingsystems yahoogroup that shows you how to do it yourself- It's in their files pages called stretching a machine - it's the Purple Monster. If you are handy, you could give it a go but like I said, I'd get a cheap kicker machine that works from a second hand store before doing it to a better machine.....