Make sure any PG or VG you buy is USP grade.
I got my DIY supplies from BlueMist Vapor. Their DIY prices are really good, and their premade juices are really cheap too.
120ml bottle of PG - $4
120ml bottle of VG - $4
120ml bottle of 60mg/ml nicotine - $28(I think)
3ml flavors - $3
They have 250+ juices and they sell the DIY flavor for everyone of their juices.
They also have an assortment of empty bottles and syringes for DIY. They also have sweetner, menthol drops, menthol crystals, and 1ml pipettes. Really everything you need to get going.
They also sell 100mg/ml nicotine, not just 60mg/ml in 3 different size bottles, and I think 36mg/ml also.
Make sure if you get 60mg/ml or 100mg/ml you MAKE SURE you are cutting it down correctly. The stuff is seriously no joke.
I recommend using a syringe at least for the nicotine so its accurate. I use syringes for all the measurings, even the flavors. THen you know everything is accurate.
The reason I say be careful using dropper bottles is because different dropper bottles give different size drops. They can be pretty big differences too. I have empty bottles from 2 different places and 1 is 18 drops for 1ml and the other is 29 drops for 1ml. If you were that far off with nicotine, that could be very dangerous. Thats why a syringe is good bc its much more accurate. If your going to only use droppers to measure at least make sure you count out how many drops it takes to equal 1ml.
I dont know about other calculators, but the one I use, E Juice Me Up, allows you to put in the number of drops that is equal to 1ml.
It will then tell you how many ml as well as how many drops of each part needed to make a juice. It works very well.