I am looking for a way to match info in Column A AND Column B, then return
the appropriate value from Column C from the same row.

Column A is "plant names" and could have 4 rows of "Holly". Column B is
"size" and would distinguish the 4 hollies by size: 1g, 5g, 7g, 10g. I want
a formula that will look up the plant name, find the correct size, and return
the value in that row from Column C ("price").

Column A is not alphabetized, and has 450-500 rows. Column B repeats the
same possible sizes throughout the column. (1g, 5g, 7g, 10g)

Is there a formula for that? Please help.