1998 Porsche Boxster Car won't start

When I get into the car to start it up, everything seems to be working fine: ie, interior lights come on; sound for keys in ignition goes off; turn the key to ACC to ON and all the dash lights come on and some go off, as expected. However, once I turn the key from ON to START, nothing happens. Literally, nothing happens. Normally if the battery were low or needed replacement, you'd hear a "click" of sorts. I don't even get that clicking sound. I get nothing at all-- no sound, no movement, no other potential diagnostic information. The battery is apparently fine since all the accessories, radio, power windows/mirrors work and even the power top goes up and down without problem. I've checked all the fuses and they're fine. The weird thing is the car had been starting fine even just 30 minutes earlier. I did something different this time around, though. Normally, I'll get in the car, start it and then plug in my cellphone. This time, I plugged my cell into the cigarette lighter, went to start the car, and NOTHING. I'm wondering if it's the starter relay, starter solenoid or the starter itself. How can I tell which one it is before having to call a wrecker and haul it to the dealer for $$$$ repairs?