I bought a 4 kit that was beyond the QB stage, with an engine in pieces (though most major parts were yellow tagged), some instruments, electric trim, and a few other goodies. It had the short gear. I paid $25k Cdn.
The fiberglass parts on these early kits was gelcoated, thick and heavy and the parts did not fit very well. Nothing like the new kits. But, they make a great flying airplane. But $12.5k is way out of line, especially if it is not built. I would think somewhere between $5k and $8k. But that is an opinion. We all know what part of the anatomy opinions are like.
The factors that made me pay $25k for mine were that it was in my city, so that saved me 1000s in transport right there, and it was built by an AME (A&P).
It all comes down to how bad you want it and how bad they want to sell it. If it is near by then you will be saving a lot of shipping/hauling costs. I would offer something considerably less, then wait patiently. Don't get emotional about it - be prepared to walk away. There are a lot of these kits that never got done. They say 80% don't get finished by the first time builder. These kits are a LOT of work. You need to be dedicated. But, many have done it, and I know very experienced military and test pilots who say the -4 is the best flying one of all the Vans airplanes. So while it is a ton of work, it is worth it.
RV 4, with an engine...and other stuff
VAF dues 2018