Lure your mother in the basement, use an excuse as "There's a leak" when she goes down the stairs, hit her in the back of the head with a blunt object. Then bound, gag and blindfold her. Lock the basement door, collect and hide all the keys towards the basement.
Now write a letter on an old typewriter (for spooky effect) about how you kidnapped your mom and demand 100.000 dollars, don't sign it of course. Fix it to the front door with a knife. Pretend to go to school, then come home just a minute after your dad. First instinct of him would be to call the police, stress him that he shouldn't, if he does proceed to call the police, he doesn't care about your mom and obviously has a mistress he loves so much more, with that information you can blackmail him but that's for another time.
In your letter the cash drop-off point should be somewhere close to home. Don't go there, go to the basement collect your mom and drug her on chloroform, then carry her with you (hence close to home) and bound her to a tree near the cash drop-off point. Wait until your father drops the cash then slice of the gag, by now she should be conscious again and screaming. Your dad will hear this and come after her. He will be occupied with crying, hugging and attempting to untie her knots.
This is your moment to grab the cash, put it in one of those 24/hr luggage lockers near you. Go home quickly. And celebrate the reunion of your family. Then a couple of weeks later proclaim you have won a price for about the same amount as the vehicle which you so desire, drop the rest of the cash in an offshore internet only savings account.
It's quick and easy really.
