I bit my nails very low until I was 17 and I got nail extensions. In those days they were made from fibreglass not acrylic and they did not harm my nails. I was a waitress at the time and I spent almost all my wages on them! But it got me out of the habit of biting my nails for several reasons; the cost and the hardness being two of them.
Oldspice maybe if you had a manicure every couple of weeks then you would see how pretty your nails could be, and the money you spend on them might be an incentive to stop biting?