We've got some more details on RocketLab's MSR proposal:

The company’s concept centers around two Neutron rockets, one launching an Earth Return Orbiter and another launching a lander carrying the Mars Ascent Vehicle.

The lander would retrieve up to 30 sample tubes from NASA’s Perseverance rover, which has been on the Martian surface since 2021, and launch them into orbit, where the Earth Return Orbiter would capture them for the journey back. Rocket Lab said it would aim to return samples as early as 2031 for under $2 billion.