Is the single click/clunk coming from a starter which is on the passenger side of the engine under the exhaust manifold? It probably is not likely the starter relay this is not very common.
90% of the time it is the starter contacts in the starter that go bad. The click sound is the solenoid engaging but the copper contacts are worn and the drive motor is unable to turn because of the loss of power. The kit can be purchased from the dealer for about $25 or just replace the starter. The starter is basically shoehorned up under the exhaust manifold and is removed through the passenger side inner fender liner well. If you have an automatic transmission you have to disconnect or unbolt the dipstick tube and cooler lines to give you a little extra to wrestle the starter out from under the engine and through the fender well.