Errrrrrr. Let's try this approach:
Welcome to MY FREEDOM SMOKES
That place sells plain PG for cutting or making nic-free juice (and also 48mg PG) in varying amounts. I don't know if it is the CHEAPEST, but the prices seem decent to me and it seems to be of good quality. Plain PG is at the bottom of the page. Of course, other places sell PG, and you can even get it at some tractor supply stores. For all I know, that is where MFS gets theirs, but somehow I feel better getting it from an e-cig place. Just personal preference! You just want to make sure it is USP / food grade. <Unless as the previous poster guessed, you meant
PV. In which case, ignore this paragraph.>
As far as the passthroughs: Yes, the battery is rechargeable, and in fact it charges while you have it plugged into a USB port. For that reason, you can also unplug it and still use it for a while. BUT, not all passthroughs have inline batteries. Those types send about 5v to your atty and you cannot unplug them and continue to use them. I prefer the inline battery type, but others prefer the no battery / 5v type because it gives a better hit due to the higher voltage. Personally, I don't want to over-volt my atty for fear of killing it sooner.
Hope this helps.