With Invisalign, how many trays can I get at one time? (Photo)

I work overseas and I’m sometimes away from home 3-6 months, sometimes more. Wanted to know is this an option for me. I would understand if this would not be an option for someone in payment plans but I’d like to pay for the whole thing at once. I had braces when I was younger but never went through the whole thing. The tops stayed pretty good but the bottoms not so good. Thank you.