Hang on a sec, it appears like you need atleast 1 base station (this is the sensor) in order to use the Index, see:
https://www.reddit.com/r/ValveIndex/comments/gv2mgf/can_the_index_run_with_base_stations_turned_off/
I know other SteamVR headsets like the Pimax’s and the Varjo’s do not need to base stations, they have internal sensors in the headset that allow 3dof (with a basestation you get 6dof), but the Index doesn’t have this it seems. If i were you I’d double check this via google searches.
All is not lost if you are really wanting an Index, the basestations can be bought new for about £149 each (you only need one). You do not need Index controllers for MSFS.
It’s correct the Index does not have the resolution of a quest 2 or especially the G2 so it might be a bit easier to power, gpu wise.
Is a gpu upgrade out of the question? The Index is relatively old tech VR wise. By the time you’ve bought an Index headset and base station, you might not have much change out of buying a better gpu (plus sell your old one) and a quest 2/G2.
I’ve never purchased an Index but have purchased 9 other headsets and the cables have been included, except for the quest 2 as that doesn’t necessarily need a cable as it can operate wirelessly and standalone (certain games - msfs isn’t 1 of them - can be installed on the headset itself).