advice picking a lens for gig videography for the canon m50 mark ii

I've been using the M50 Mark ii with the kit lens for a little over a year now, I've found that for most of what I get up to I haven't needed any new equipment or lenses however pretty soon I'm shooting some live footage of my friend's band and decided to buy a new lens to mark the occasion, it's a pretty small venue and will be quite dark so I reckon ill need something with a faster speed like an f/2 or 1.8 however I'm feeling a little lost on what mm of lens I should buy as well as brands (money's a little tight so ill be buying used, preferably £200 or under) if anyone has any recommendations it would be greatly appreciated :)