I love solutions to problems which involve a cardboard box - i.e cheap as hell. You may have seen my spray booth. In this vid - link below - a maker, Ricky Impey, has fabbed a filament dryer. Reuse the box the filament came in, cut off the bottom, poke 9 holes in the top, and then you put the filament under the new box 'lid' and turn on the heat bed on your printer 70C. Wait. Monitor. Love it. The little electronic humidity gauges are cheap on ebay or amazon. Ricky you rock.