If you are exhausting to the outside you shouldn't need the carbon filter.
The fiber filter should last for at least 3 or 4 models or more I would think, but of course that all depends on how much paint you blast into the booth. The filters tend to clog around the opening to the fan mostly and the rest of the filter stays clean. At least that is how it is on my Badger spray booth.
You may be able to find furnace filters at Walmart that could fit it depending on it's size.
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon