I feel your pain, as it's my pain too.

Right now we have a pool of gitlab runners running as dedicated virtual machines but on the to-do list I have to test whether rootless podman + gitlab runner cache + $DOCKER_HOST pointing to podman's sock file can let developers use plain old docker-compose and the general docker tooling... Within a dumb pod in a kubernetes clusters, with all the bells and whistles (especially cluster autoscaling).

A man can dream.

Edit: we are a bit advantaged because we run on openstack, run our own registry (harbor) and our cloud provider doesn't charge us for bandwidth...