Eufloria HD is a minimal real time strategy game that costs $4.99 and has zero in app purchases.
Pro Multiple game modes
Eufloria has a three modes. Two of them, "Skirmish Arena" & "Dark Matter" are unlocked after completing the Campaign mode. "Skirmish Arena" has 8 maps to to test your skills against AI, and "Dark Matter" takes certain maps from the Campaign, changes the aesthetic and increases the difficulty.