You can draw out all refrigerant from a system with no expensive equipment. All you need is a hose (preferably with manifold gauge), a suitable storage tank, a decently insulated container (like a large cooler) that it fits mostly inside, and dry ice to pack around it, around 10 pounds, or less if you have a liquid acetone or alcohol bath to transfer the heat more efficiently out of the tank. Dry ice is around -70°C, and automotive refrigerants liquefy around -25-30°C, so all (modulo some extremely low vapor pressure) the refrigerant will liquefy in the tank; you can confirm this by observing vacuum on your manifold gauges, which should match the vapor pressure of your refrigerant at whatever temperature you can get the tank down to.
Dry ice will run you about $2/lb and can be purchased at Kroger and some other grocery stores.
You can get a 30 lb tank for around $80-100. I got one off Amazon. In theory, if you have an empty refill tank that can hold at least as much as your system, you could use it. This is of questionable legality, and dangerous if there's any risk you might overfill it (assuming it might return to a gaseous state before you move it back, in which case an overfilled tank could explode), but it's not as bad as actually pumping hot pressurized gas into such a tank.
Here's a picture of the setup I've used, in progress: