MM6 Limited Edition (including MM1-5): Deutsch, English: $2.49 (-75%)
MM7: Deutsch, English, français: $1.49 (-75%)
MM8: Deutsch, English, français: $1.49 (-75%)
MM9: English: $1.49 (-75%)
HoMM1: Deutsch, English, français: $4.99 (-50%)
HoMM2 Gold: Deutsch, English, français: $4.99 (-50%)
HoMM3 Complete: English, français: $4.99 (-50%)
HoMM4 Complete: Deutsch, English, español, français, italiano: $4.99 (-50%)
HoMM5 Bundle: Deutsch, English, español, français, italiano: $9.99 (-50%)
Heroes Chronicles All: English: $4.99 (-50%)
All prices are in USD.
A purchased game includes all available language versions. To download a non-English version's installer, click the game in "My collection" and change its "LANG" before downloading the installer.
For those who play MM678 merge, it would be necessary to purchase MM8, and good to also purchase MM6 and 7 to avoid any possible copyright issue.
If you buy the Heroes SERIES which includes all these Heroes games listed, then you will get a -66% discount instead of -50%. It seems such further discount doesn't apply to MM6-9 SERIES this time (during the 2017 Black Friday sale, MM6-9 SERIES had a -85% discount)
This post has been rewritten on June 6 2018, the previous version posted on Nov 21 2017 during the 2017 Black Friday sale is as following (and you can see although Summer Sale is good, it is not as good as Black Friday sale, so feel free to wait for the 2018 Black Friday sale):
MM6-9 have a really attractive price on GOG.com during its Black Friday sale, which is ongoing and will end on November 28, 11PM UTC. HoMM1-5's discount is also available but a little less attractive.
MM6 Limited Edition (including MM1-5): Deutsch, English: $1.49
MM7: Deutsch, English, français: $0.89
MM8: Deutsch, English, français: $0.89
MM9: English: $0.89
HoMM1: Deutsch, English, français: $2.49
HoMM2 Gold: Deutsch, English, français: $2.49
HoMM3 Complete: English, français: $2.49
HoMM4 Complete: Deutsch, English, español, français, italiano: $2.49
HoMM5 Bundle: Deutsch, English, español, français, italiano: $4.99
Heroes Chronicles All: English: $2.49
You might initially see a price of $2.49 for MM6 and $1.49 for MM7-9 (75% discount). However, after logging in (or maybe after putting the game into the cart), you will have a 85% discount ($1.49 for MM6, $0.89 for MM7-9).