If you use them, they wear out. If you don't sharpen them as often as you should, they then become "taper-length" drills because the lands near the cutting end are smaller than the drill lands farther up. Then, they squeak when drilling deep holes, and score the hell out of the side of the hole, but you already knew that.
Cheap drills seem to abound nowadays, and some cheap sets seem to be of decent quality. I stock up regularly on TIN coated 29 piece sets at anywhere from $35 to $65 CDN and they seem to be decent for general purpose usage. Your mileage may vary. $30 for a 115 piece set is pretty cheap, even the box is worth more than that