Should I even bother using a prepare cache statement for the query?

That depends on whether or not you're executing the statement multiple times. In MySQL, you get less benefit in pre-preparing your statements than in some other databases, but the answer is that you can prepare it once if you want to since selectrow_array() (which there are other examples of in this thread) accepts either a SQL statement or a previously prepared statement handle as it's first argument.

Also, depending on how often you're executing the lookup in your program, and how large the table is, you may want to just read the whole table into a hash array.