Do not close buds in a jar at 70%, <67% is ok and <65% is even better. Heavy duty Brown Paper Bags Like from the grocery store is what has worked best for me. Your RH environment must be lower than the buds to dry - period. Yes it costs a lot to run a dehumidifier but how much is the bud worth.
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This is the dehumidifier I own and use. In a 10x15 room I can get the RH down to 40% when the outdoors is in the 80%s. I have to dump the thing 4 or 5 times a day when conditions are like that.
If you have a "Frost Free" refrigerator it will work over a longer period. If it is not frost free forget it.
The life of a farmer is never easy or cheap.