How much RAM/VCPUs have people found give best price/performance for a docker container doing one hourly elt then disappearing, eg. salesfroce to redshift?

No concrete numbers but I guess if your tap or target does some amount of preprocessing/transformation, it will be memory intensive. For example, datamill's targets unnest streams and use quite a lot of memory. There's also a balance between max memory usage and batch size: the larger your batch the more memory you need. Otherwise if they're passing records in the most lazy way possible (i.e. Python generators only), they'll be more CPU intensive.