If include the "old days" of the late 80's/Early 90's when I started collecting, the bargains were many, here are some examples.
My Blue Snaggletooth came from a collection that I got from a guy that was working at the same comic book store I was. He sold me all of his figures for 50 cents each. This was in 1988 or 1989.
First MOC figures came from Toys R Us on the clearance shelf, .97 each, Weequay, Lobot (on a tattered ESB card), AT-ST Driver (still have this one), Nikto (still have this one), and a few others, think there were seven total. Somewhere around 1988 or so.
Droids Kez Iban and Jord Dusat in a clearance bin at KayBee toys for 50 cents each. No one cared about Ewoks and Droids in the early days. Around 1990.
POTF carded B-Wing Pilots first for $3, then later for $2, and finally found the true source and got them for $1 each, in case lots of 96 pieces. Longer story about these that I will try to tell on here sometime. This was in 1990-1991.
TriLogo Yoda, Darth Vader, and a few others for $3 each from a mail order catalog in 1988.
POTF carded Luke Stormtrooper for $22, Droids Carded R2-D2's for $12 1990 or so.
Lots of MOC figures for $3 to $5 at local toy shows 1988 to 1992.
Huge amounts of bagged figures 50 cents to $1 each. Several stories about these, as well.
The thread topic says "Best Ever bargain", but I don't know which one to pick.
Sadly these days are long gone, but I've managed to keep some of the items in my current collection.