people dont really understand what the differences are between different octanes. It used to be detergents were different now those are standard across the board.
However your car's compression ratio is around 10.5:1 if i remember correctly. With a lower compression engine say 8:1 you can use a lower octane fuel due to less heat being created. Since a higher octane fuel doesn't ignite until later in the compression cycle it will withstand a higher temperature. Putting a lower octane fuel in your higher compression engine can cause knock and detonation, yes you have knock sensors though they cant always catch it in time and you could blow a rod thru the block. Unlikely but ive seen it happen.
the main thing you'll run into like others have said is decreased fuel milage. You'll get more carbon build up as in over time your motor will fill with carbon deposits(see image below) Now at first ya carbon deposits are normal and can be ok to an extent though after time they will build up to an extent of raising your compression ratio and making things completely different
So summary ya you might be saving a couple bucks cause every time you are buying gas though you are spending more since gas milage is decreased, over time causing more harm than good, and if you cant afford it dont drive it