You're right, we didn't. But that's where he ended up and it was four seasons ago. Salaries have escalated since then.
I'm not sure how wins relate to salary but we're apparently willing to pay $30M for a guy who's expected to win 20 games. That's $1.5M per win. If we get 8-10 wins from Buch - which isn't an unreasonable expectation over the full season - that's the same ratio Price is getting.
Equally as important is the fact that he doesn't overburden a team with losses - and that's important. We may be able to pick up a pitcher at a lower salary who'll win those 8-10 games, but at the same time he may lose 15 games doing it where Buch may lose "only" 8-10. Sure, that makes Buch a .500 pitcher over a half season but this other guy has given us 5 more losses, and when a division championship is won by only a game or three, five is a big number.
And... there's always the potential that Buch is going to win 17-18 which is a better potential than that guy whom we picked up at half the cost.