Is CS2 FPS Benchmark Map free?

Yes. CS2 FPS Benchmark Map is released under Community / Steam Workshop and costs nothing. Neither it nor Counter-Strike 2 has any paid content.

What do I need to run CS2 FPS Benchmark Map?

Counter-Strike 2, which is itself free. CS2 FPS Benchmark Map is an add-on and will not run standalone.

The PlayBound Launcher installs it in one click from Counter-Strike 2's mods list. You can also install it by hand — full steps are on this page.

Roughly 60 MB, on top of the base Counter-Strike 2 installation.

CS2 FPS Benchmark Map — Free Counter-Strike 2 Mod · PlayBound