Trophies are a number, not an arena
This page targets a trophy count. If you want to hit a round personal best, a badge or leaderboard figure, or the exact number that unlocks Ranked, you pick the target number and the calculator prices the push from your current trophies to that figure — the per-trophy rate rises as you climb into the higher bands, so a push at 9,000 costs more per 100 trophies than one at 2,000. That's different from a targeted arena boost, which cares about reaching a named arena for its card and chest unlocks, and from a Ranked Mode league climb, where trophies don't count at all.