Dai and Abu,
I really don't know what a full kit would cost and may be way off at $900. But if just ribs and formers are $200-300 then a full kit still may be twice that,
I agree with Abu that the term "scratch built" should be left for doing the whole project. Research, drawing plans, cutting parts, building and finishing detail. Even then you'll do some experimenting as you work, and will use your ideas and those of others to make decisions about how to do things.
For example when I was 12 years old I knew about soaking strips of wood, bending them round a form with glue between the strips, pinning them down and letting them dry. I don't think I invented that. But I've seen that method described in articles over and over through the years. As Abu has said we build on each other's experiences.
How hard that is depends on the aircraft. I've built fun-fly /trainers without plans by just "throwing them together". I guess that's scratch built. But leave the term alone and just go over in your head what you think you'll have to do, and that will tell you if you want to start or not.

alan