From MaGog's logs for 13 January:
NOTE! CHANGED King's Bounty: Dark Side, reg_price_au: undef ***TO*** 14.89
NOTE! CHANGED King's Bounty: Dark Side, reg_price_de: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, reg_price_gb: undef ***TO*** 20.29
NOTE! CHANGED King's Bounty: Dark Side, reg_price_pl: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, reg_price_ru: undef ***TO*** 5.69
NOTE! CHANGED King's Bounty: Dark Side, reg_price_ch: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, reg_price_cz: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, reg_price_no: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, reg_price_se: undef ***TO*** 19.99
NOTE! CHANGED King's Bounty: Dark Side, regional_str: undef ***TO*** AU,DE,GB,PL,RU,CH,CZ,NO,SE,
[US price is $15.99]
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_au: undef ***TO*** 19.09
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_de: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_gb: undef ***TO*** 24.99
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_pl: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_ru: undef ***TO*** 6.89
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_ch: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_cz: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_no: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, reg_price_se: undef ***TO*** 25.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition, regional_str: undef ***TO*** AU,DE,GB,PL,RU,CH,CZ,NO,SE,
[US price is $19.99]
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_au: undef ***TO*** 6.19
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_de: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_gb: undef ***TO*** 6.99
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_pl: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_ru: undef ***TO*** 1.69
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_ch: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_cz: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_no: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, reg_price_se: undef ***TO*** 7.39
NOTE! CHANGED King's Bounty: Dark Side - Premium Edition Upgrade, regional_str: undef ***TO*** AU,DE,GB,PL,RU,CH,CZ,NO,SE,
[US price is $5.99]
Already reported by Grargar.
Note that for AU (Australia and New Zealand), the game itself is cheaper than US, but the DLC is more expensive.