Could be something as simple as a clutch switch ( $10 to $25 ) if you have a manual transmission or could be your ignition switch $68 at the dealer and it looks like a couple hours to replace, Hope this helps
It sounds like it's time for a check of your battery and starter. either one could cause the problem you describe. Your local auto parts store may test your battery for you - testing the starter is a bit more complex. You may need some help with that one. If the starter and battery both check out OK you will need to dig deeper into the starting systems to try and find the problem.