I built a slow build RV-7 and guess I've gone through about half a dozen cobalt #40 drills and about 4 #30 drills. If you get cobalt aircraft drills you'll never be able to justify needing a drill sharpener, let alone the frustration of not having a perfectly ground and easy to control bit. A roofer here told me that drilling steel roofing sheeting they would go through half a dozen drill bits a day, at $6 each. I told him I could get some cobalt aircraft drills for him, and because they were so cheap, he ordered 50. I saw him a few months later and asked how they were working. He was still on his first cobalt drill. I guess he's got himself a couple of lifetimes worth.
I have developed a policy of only buying cobalt bits, and when I'm no longer happy with they performance, I retire them to the tractor workshop on the farm where the mechanic can sharpen them on a grinding wheel and continue to use them on farm machinery. Knowing I can keep a bit centered and not botch a part is far more important than saving a couple of dollars on bits.
Tom.