The generally recommended RDA for flavor testing is the Oumier Wasp Nano. It's single coil (which means it's quite easy to build) and has a small chamber (which improves flavor purity). You can buy it from pretty much any vape site for $10-20.
For single flavor tests, plain 26 ga stainless steel wire works fine. You can buy 100 feet for about $7 from Amazon.
You'll also need cotton. You can buy Muji cotton super cheap from Amazon. This amount of cotton should last years.
As for tools, a 3 mm drill bit (to wrap the wire around), wire clippers, and sharp scissors (to cut the cotton) is really all you need, but if you wanna get into rebuildable you can always buy a coil building kit.
Other than that, YouTube videos are your best friend!