I remember when I hosted a DM where people had to run around and find weapons, due to random spawning, knowledge of weapon and powerup locations, and due to player having to race to certain weapons, it turned out to be a lot of fun and seemed a bit fair, FYI the weapons were old, like the Mac-10, ephi's shotguns, kaje's minigun, etc.
As for buy able weapons I think they suit zombie servers more, heck in the non-BL game Killing Floor it works out pretty dam well, maybe perhaps someone should try that? Or on death you lose money like Counter Strike.
Oh and another thing:
People need to test their TDMs beforehand and listen to their player base so it can be fair, however as long as they don't take idiotic suggestions.