Does the starter have a separate fuse? If so, that's your cheapest option! Otherwise I can only think of a jammed starter (unusual these days) or kaput starter solenoid. Do the panel lights dim when the starter is turned?
Make sure everything else is turned off when you start the car to minimise drain on the battery.
On modern cars if the battery is on it's way out the ecu will not let you start the car even if lights and other electrics work, check the battery first.