If you drill a lot of holes a drill sharpener will pay for itself very quickly. You save not only the cost of the bit, but also the time saved by using a sharp bit instead of making do with a worn one.
Btw, one of the quickest ways to wear a drill bit is by using it at too high a speed or with not enough feed pressure. A drill bit stays sharper if it's cutting, as opposed to rubbing over the surface. Look at your chips as they come out from the flutes. If they're thick and long the the drill is cutting properly. If they're like powder, then the drill is too dull, or your drilling at too high a speed. Once the chips turn to powder, the bit is useless for further cutting.
Drill bits are not surface hardened, so you will not lower the hardness by resharpening it, as long as you do not overheat the bit during the resharpening process.
Drill bit sharpeners come in all price ranges. I have one that cost $6500.00 when new. I found it at an auction and paid $75.00 for it. It was missing the tailstock, but that was easily remedied with a chunk of alum. and a few hours on the milling machine. This sharpener puts a grind on a drill bit that is better then the factory grind. In fact, I often use it to regrind a new drill bit before use.
The problem with the real cheap drill sharpeners (the $29.00 units) is they don't put the proper relief angle on the bit. The drill doctor units are about the cheapest you can buy that will make a decent regrind. But I have also heard some complaints about the lower line drill doctor, the one that sells for around $130.00. I've never used one myself, but I've heard of guys returning it because the chuck flexes a lot, which makes it hard to get an accurate grind. If the two cutting flutes are not ground exactly the same, the drill will walk off to the side when cutting.
Drill doctor makes a number of different models, and IIRC, the decent ones go for about $500.00 and up. You can often find drill sharpeners on ebay, but even there you usually have to pay a pretty good penny for a decent one.
FWIW,
Dave