This is what we use:
RTape ApliTape 4000 is a standard paper application tape with a low tack rubber adhesive. It's easy to unroll and apply by either hand or machine. RTape ApliTape 4000 releases, tears, and cuts cleanly with no build up of tackiness over time.
www.specialty-graphics.com
We usually keep it in widths from 6 inches to 24 inches. It is low tack, so it's not a struggle pulling it off. If you are careful applying it, is also works very well (after laser scoring) as a pattern masking for spraying finishes, (not super pedal applicable, but I do this sometimes). Masking tape will work, obviously a nice wide roll is easier to deal with. The basic caveat—do a test run with whatever you're planning to use, just to make sure there are no "surprises."
Yeah, big cost difference between extruded and cel cast. There's some "in-between" type, called "continuous casted" that really is closer to extruded. Besides cost, the other advantage extruded has is that it is closer tolerances thickness. Cell cast is all over the place, which if you're building with it can be a real problem. But there are so many issues working with extruded, that it just wasn't cost effective for the processes that we use mostly (machining, laser cutting, heat forming).