For economy buy bulk and "jug" them. Mold should not be a problem if you are using sterile jars with fresh lids. Given the availability of canning jars, do not try re-using things like mayonnaise jars. The lids on commercial food jars were never intended sterilization and re-use. They tend to use things like waxed cardboard for the lid liner, were intended to be refrigerated after opening, and for short term storage. If you are using Canning jars make sure you clean them well, and then make sure nothing like the dishwashing detergent is left in them even in trace amounts, tobacco absorbs scents like crazy, and most do not like soapy tobacco. Also splurge and get new lids or for the "bailer" type jars (my favourites) get new sealing rings.
I have never had a jarred tobacco go moldy on me (so far, knock on wood). The closer the jar is to the amount of tobacco the less exposure to air you have, the less you will lose of any flavour. New canning jars are cheap enough, but you can get them even cheaper, they can be found at nearly estate or downsizing moving sale in the rural or small towns. Think about, every little old lady who is moving from her empty nest to an apartment or a seniors residence has boxes of these jars, i seldom pay more than about a quarter for a jar, buying them a box at a time (generally 12 to a box).
Al (in Canada)