The usual word to "use in place of opposite" when speaking of words is antonym, "A word which has the opposite meaning of another, although not necessarily in all its senses."
Regarding an antonym of insatiable, satiable is indeed a word, and per wiktionary it means
Capable of being sated, satisfiable. (eg) The god's demand for blood was satiable only by the sacrifice of a virgin.
However, satiable does not fit appropriately into your example sentence; instead try a word like bottomless, endless, unfathomed, bountiful, or overflowing or previously-suggested inexhaustible if you mean that your funding will never run out.