Seconding @crenquis’ Wiha recommendation. Another option is professional jewelers’ supplies, such as http://www.riogrande.com/Search/screwdriver — Which are also not cheap, but I suspect that in addition to being more fragile and generally crappy, cheap tools are more easily lost because the owner doesn’t treasure them. Like most people, I used to regularly leave umbrellas god-knows-where, couldn’t hold on to one for more than a month, until I finally got a nice umbrella. I’ve had it for years now.
ETA: Fuck those stupid plastic cases. Get or make a tiny tool roll if the drivers don’t come with one. You can make the whole thing out of duct tape and thread.