Great question! I had 3 choices. All three would have worked.
1). I could have put a lot of time into lapping them, and truthfully, I did start on a couple and they were coming along ok. But, there was a "edge" or "lip" I didn't really care for too much. I would have done this route if the money was more restricted.
2). I called a local performance machine shop, and they wanted between 25 - 30 bucks to grind them. They could have cleaned them up pretty nice I imagine. This would have been a cheaper route, but not that far away from new.
3). New was about 55 bucks at my door. I had pretty much bought all the components for the build, and there was room for them in the budget.
My thought process was the exhaust valves were 40 years old and had 120,000 miles on them. The exhaust valves take a beaten. Means the funds allowed it, why not new?