I get my nic from MyFreedomSmokes.Com and have never had a reason to want to pay more than their $50/liter for 100mg concentrate at their every day price. If you are not comfortable at first working with 100mg concentrate they also have good prices on 24mg, for example.
I have bought VG from Bulk Apothecary, Essential Depot and MFS. All tasted the same to me. I found BA to have the best price for a gallon, and ED the best price for 2 gallons. Amazon has a very good price on ED in quarts, especially if you happen to have Amazon Prime. Shipping is a big part of the cost so factor that in. I use very little PG and probably still on my original liter from MFS a year later.
For flavorings, I concentrated on the big TFA thread in the DIY sub forum. I used mainly Bill's Magic Vapor's recipes, which are all high flavor mixes that require little or no steeping. I highly recommend that approach because you get instant gratification and feedback instead waiting weeks for your concoctions to steep.
The way I did my flavorings was mainly sourcing 8ml sample vials from Wizard Labs. I used those sample vials to find the recipes and flavorings I liked. Then I bought my most needed flavors direct from TFA in 4 oz botles. You have to sign up for their bulk flavoring account but it's easy. You can also get TFA 4 oz and other put ups from many other sources but I decided it was probably best and often cheapest to go direct to TFA.
The economics of juice is that unflavored base, bought correctly, will cost you around 1 cent/milliliter. That's 30 cents for a one ounce bottle. In particular nic is cheap now, but it is not likely to stay that way so I would suggest stocking up with a few liters as soon as you are comfortable working with concentrate.
The cost is all in the flavorings. To do a 30% high flavor mix, for example, your cost will go to about 3.5 cents/ml. And that doesn't count inventorying a growing pile of flavors. I spent about $500 rather quickly just accumulating mainly sample bottles of about 100 flavors so you have to be careful unless you are looking for a new moderately expensive hobby
Those 8ml sample bottles from Wizard Labs cost $1.49 each. An ounce of TFA will run you about $4.50 - $5.00. A 4 oz bottle direct from TFA will run $6 - $10 or so. For an extra couple bucks you get 4x the flavoring.
Once you DIY you will never look back. Not only do you save money but you get total control over exactly what you vape and come to understand eJuice in a way you cannot otherwise do. And it takes all the mystery and magic out of it.