There is no such thing as a regas, it's a sealed system, if it needs gas it's because something is rooted, it needs repairing and regassing afterwards.
Fancy ac machines are definitely not required, we've used them at work and always go back to a basic trolley setup with manifold/gauge set, vac pump, recovery unit, scales and ac gas/nitrogen bottles etc. Simple and reliable.
I've only ever done ac on the same vehicles, 70 series Landcruisers due to working in an underground mine and in my experience the difference in variances of oil one to the next has had no measurable effect on operation, ie measuring to the exact ml of oil is not the end of the world.