Just a quick glance, it looks like Linmar has the cheapest, but I've never used. No idea if it is any good. I use m-f's super soft.
I have purchased and used two one gallon jugs for my and son's separate use.
I highly recommend them for cost and rather quick shipping.
Just remember to shake well before using.
Good luck. It has become quite addictive and using re-melts is also good and economic.