Tomato-tomato potato-potato

Ok, how do you say this word:

Finance

well?

I say finance like FI-nance (with the "i" pronounced like it is in "I" "nice" or "high")

Several people that I've heard recently say Fi-NANCE (with the "i" pronounced like it is in "fin" or "swim")

This reminded me of the word "sugar." In the cooking class in HK, our cooking prof. pronounced like it real should be pronounced (but isn't) where the "s" actually makes an "s" sound. Why do we pronounce "s" as "sh" in this word? I was trying to think of other words like this but couldn't think of any. I wonder why it changes...