The Viscount "value" (I use that term loosely) garage has machines you use when leaving, before you get back to your car. I believe they accept debit, and definitely credit. I don't think they take cash (could be wrong).
I think the Viscount outside "value" lot is still manned by a person so you can pay cash if you want (probably credit, maybe debit)
Sorry I don't have more concrete info on the outside lot, I only use the garage now, especially in the winter. I'll pay the $20 to avoid coming back to a car heaped with snow.
I much prefer the monorail train to any shuttle bus. It is prompt and keeps you inside the whole way, so no standing outside in your spring jacket in -20C temperatures. It services both terminals so it doesn't matter if you leave from one and come back to a different terminal.