How long does it take to farm 100 exalted orbs?

you can farm up enough currency for an exalt in i'd say on average 2 hours.
most likely something like 1-1.5 hours for an exalt if you're liquidating everything to in order to get em. so 100 exalts probably 100-200 hours without getting really lucky on something like a great uber enchant or something.

i like to run a build that can operate on a budget, then i use it to farm up currency to get the real optimal shit

If you are just going to purely farm them from enemies...

I started playing this game in 2013 and had been purely SSF since then.

According to my stash i have 43 ex.