Very short-pull derailleurs designed specifically for 1x6 drivetrains?
In theory you could get a short-cage derailleur, but that would add significantly to the parts cost and not really be much better.

Back when I did a lot of fixups, it was all about making the bike as good as it could be, without spending anything on the more expensive items.  We'd often replace brake pads and cables with new, but items like cassettes and derailleurs were very rarely bought new.

Fixups are a different mindset to working on your own bike.

Instead, we'd knock down bikes that were too-far-gone, and put the usable bits into storage bins.  During downtime, volunteers would clean and recondition components, then return them to storage.  So later, if someone's fixing a bike and finds they need a rear mech, they'd pull one from the parts storage bin for rear mechs and fit it up.  The old part would be either cleaned and serviced, or scrapped for metals which earned a couple hundred dollars perhaps twice a year, but each time it was a truckload of pre-sorted metals.

The expertise comes from deciding how dead a bike has to be to go to parting-out vs what's worth saving.  That is affected by how busy the operation is, what parts are low-stock.  Your local area also affects the supply line - there are always old bikes turning up.  And finally the ultimate limiter is how much space you have for storage.