The amount of savings (assets) you need depends on the difference between your fiance's income and 125% of the poverty line. What is his income amount?
Why would there be a big deposit? Be careful here, if you are talking about having someone else deposit money into an account temporarily for immigration purposes and then withdrawing it later on, you might run into legal ramifications.
If you have a cosponsor, your cosponsor needs to prove they have income that meets or exceeds 125% of the poverty line. Cosponsors cannot use assets to qualify.