If complete means with extractor and spring, then the cost grows. Most bolt heads that are offered for sale have been stripped... As stated, the No 3 head commands a premium say ~ 80$. I picked up a No4 Mk1 last year (attic find in a cottage), that had a No 4 bolt head. I had to look at it closely, and finally measure it to be sure. I got my headspace gages out and found that the rifle wouldnt close on a go, but would do so with a No 2 bolt head. The rifle had been set up for target shooting, I suspect that someone had decided to tighten the headspace for accuracy purposes...