We really didn't understand this rule (page 7 of the manual): "3 x Ancient Technology: you may take the cheapest Technology Tile you don't already have...". How do you decide what is the cheapest?
The "cheapest Technology Tile" is counted according to the technology's base price; technology discounts are irrelevant. Ergo, of all the available technology tiles, you pick the one (that you don't already have) that is left-most on the track.
If there's more than one "cheapest" technology available (i.e. multiple technologies in the left-most column), you can take your pick of them.