starting problems

2000 Sienna LE 175K miles.

I've been having starting problems. Turning the key just makes a
clicking noise from the engine compartment. You have to turn it many
times before the engine finally turns over. This is intermittant, but
it's done it twice today. Usually it fires right up with no problem.

The battery was replaced last year and electrical system checks by
Advance Auto indicate all is well. Is it worth replacing the starter
myself or should I take it to the mechanic?