What is the best way to dry filament?
If we think about drying as a process, then we need to consider some factors:


we need to get same humidity level on the spool
that will require a good stable temperature and an air rotation (fan)
then we need to store  spool in a dry area (a bag and silicone sachets will do the work)


As energy consumption by owen could be the case, if we will run it for 4h full steam, then considering that we shall have about 60 degC, will turn down the usage by at least 70%, so we could assume that 2kW heater will be on only 30% of the time (so it will be 2kw*0.3 = 0.6kW, multiply by 4h -> we have 2.4kWh, so that is about 50 cents).

If you consider the price of wasted filament - then adding 50 cents to the drying process is something that is cheap enough to save precious nylon.