Prices grabbed from splintercards.com. This shows what kind of premium you pay buying the gold foil version of each Chaos Legion Summoner at max level compared to the regular foil.
Quix max $299.09
Quix GF Max $836
2.79X
Thaddius Brood MAX $293.135
Thaddius Brood GF Max $664
2.26X
General Sloan Max $251.85
General Sloan GF Max $547
2.17X
OBSIDIAN Max $324.3
OBSIDIAN GF MAX $850
2.62X
KELYA FRENDUL MAX $435.85
KELYA FRENDUL GF MAX $791.5
1.81X
TARSA MAX $323.15
TARSA GF MAX $643.5
1.99X
Regular max full $1927.375
GF max full $4332
2.247X