Man, I'm sorry you've had such a miserable experience with the car. It's a shame you didn't find us before you bought it - we could have told you and SVX was not going to be as reliable as a Legacy.
Earl already gave you good advice concerning a dealer-sourced replacement. I agree with him, unless you happen to be so inclined to do it yourself. I bought a used transmission from another member on this site and installed it myself. I think I paid somewhere around $700. But, again, you have to be familiar with the car and have some experience to undertake a repair like this.
The five-speed route is certainly a step beyond a straight replacement. The transmission may bolt up, but there's still some custom fabrication and tweaking involved. It'd be tough to find a shop who would do it, and even then it'd cost a
lot. The vast majority of the five speeds I know of were installed by their owners or mechanic friends.
I'm glad you joined the site, but I'm sorry you're having these problems with the car. Let us know if there's anything else we can do to help, and let us know what you decide and how it works out for you.