Ask HN: What under $100 item has had a disproportionate impact on your life?

My $40 iPod shuffle provides energy and entertainment for my long workouts. Its great and helped me lose a lot of weight. Super durable and practical. Highly recommended.

Under $20? Condoms. Shower mat that feels like grass. Hand chalk.

Under $50? Bicycle lock. Iron skillet.

Under $100? Bicycle helmet. Bicycle headlight. Cell phone.

Under bed storage tray, old bed sheet, bag of play sand = indoor play area that's had hundreds of hours of use.