You will need:
Nicotine solution: Wizard Labs, Nude Nicotine, MyFreedonSmokes, RTS Vapes, others. You can get a small (15ml) nic sample from Nude Nicotine for "free" with only $2 shipping.
Propylene Glycol (PG) and/or
Vegetable Glycerine (VG): can get from the same suppliers as above, or Essential Depot (on their own site or via amazon) or Bulk Apothecary
Flavor concentrates: often available from the nic suppliers, or Bull City Vapor, OSDIYS (One-Stop DIY Shop), or direct from manufacturer (Flavour Art, The Flavor Apprentice/The Perfumer's Apprentice, Hangsen, Inawera are all popular brands)
Glass/plastic bottles to store your materials and finished liquids: eBay, Amazon, specialtybottle.com, packagingoptionsdirect.com
Measuring equipment: many people use syringes and blunt-tipped industrial filling needles (available from most of the sources listed above) but I, and many others, have made the switch to mixing by weight. You'll need to transfer your materials to plastic squeeze bottles and/or get some disposable pipettes (eBay/amazon) and a 0.01g digital scale like
this one from eBay or
this one from Amaon.
How much it costs depends on how deep you want to go. I got started with just a few flavors, a few bottles and syringes, and a small amount of nic/PG/VG for about $40 and it lasted me a couple months, but if you really just want to get your toes wet and see if it's for you, you can probably squeak by with just the bare minimum on like $25 or less. Since then I've spent about another $120 or so and I have enough now to last me for about two more years without buying anything more except maybe some more VG/PG (at, like, $12/qt or even less when you buy them in bulk) unless I go crazy trying out a bunch of new flavors.