I bought a bottle of silica gel (about 1kg) and packed it into a porous paper bag (takes about 500g) to store in an airtight dry box. I did this 5 years ago. About once a year when I see the gel become white and pinkish I will take it out and bake it in my oven until it becomes dark blue again, and then back it goes into the case. I have been recycling this gel for all these years and it has been a very economical way to keep your equipment dry. I have had mixed results. I got a digital P&S and so was lazy to use my SLR for 2 years. As a result I did not touch the lenses for 2 years but kept it in the dry box. Surprisingly I did not have any major fungus problem when I took it out to check last night. The down side is that I realised the skin on my old SLR has cracked a little and some of it has peeled off. Its not that bad, only on the surface.
This is very economical and you can recycle the gel but its tough to control the exact humidity level.