A label for 30 minutes on the dial doesn't mean a meter has the best low light measuring capacity. Look for specs that show the lowest EV to which the meter can accurately measure. The LunaPro series are among the best, especially the LunaPro SBC (US market model name, Profisix in others) which goes to about EV -4, and perhaps some later models that I'm not that familiar with. Other brands have a few models that go low, but Gossen seems to be ahead in that area across models. You should be able to find specifications.

As others have said, by 30 minutes metered exposure time you're running into serious reciprocity failure with pretty much all films. Use Fuji Acros if you want to minimize that in B&W. No commercial meter I've seen is set up to calculate reciprocity failure, and that varies radically across films anyway. Your best bet is to read up on reciprocity failure and how to calculate it (plenty of that here on APUG), find a film to stick with, make notes based on your experience, and keep a printed table of adjustments, either by opening up aperture or lengthening exposure. Note that extending exposure time involves a compounding effect, just like compound interest.

You can't make it as simple as you seem to want and still have the accuracy you desire. Mentioning the kind of film you want to use could probably bring recommendations for lowest reciprocity failure. B&W, color negative, color transparency? There is also the problem of color shift if you're using color, caused by different reciprocity characteristics in the different color layers.

Lee