You can get DX-coded cartridges, too. I've seen them in both ISO 100 and 400. The labels are cheaper than the cartridges, but not much cheaper.
Of course, as you mentioned, if your camera defaults to 100 then there is no need for the 100 ones.
As an option, you could always dial in compensation. If you're shooting ISO 200, shoot it in a naked cartridge and dial in -1 stop.
Another option, as silly as it sounds... get a camera with manual ISO settings. They are dirt cheap now. Even the lowly Nikon F50 permits manual ISO setting. The F70 does as well. Neither will cost you a hundred bucks - probably a lot less than that. It's surprising what $35 or $50 will get you in a camera.