What is the best way to dry filament? I have some nylon that appears to have soaked up some moisture, the prints have the texture of rice bubbles. So I'm wondering what people suggest for drying.

My priorities are:


cheap
low energy use
safe
effective


I know you can put it in the oven for four hours, but that's going to chew up a lot of electricity. 

I have been leaving the spool in front of a fan heater, since the heater is on anyway, it probably only gets to 40°-50°, but since my kids spend all day sitting in front of the heater I can leave it there for an extended amount of time. Anyone have success with this method?

I had considered putting it in my car. I know even on cool days it gets pretty warm in there, but I'm not sure whether that would translate to low humidity.
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.