M&M Clash of Heroes is a strategy puzzle RPG based on the Might and Magic series that costs $4.99 and has zero in app purchases.
Pro Combat involves a reasonable amount of strategy
By using many different mechanics such as charge timers for moves as well as matching and moving certain groups on a field in order to perform defensive or offensive maneuvers allows for many different strategies that can be used to win a battle. For what is essentially a match-3 game the level of planning that can be used is pretty deep.
Pro Lengthy campaign
M&M Clash of Heroes has a lengthy campaign, even for console standards. Clocking in at around 24 hours to beat the game it will provide a tons of playtime that for the cost of $4.99 is difficult to find anything on mobile comparable with that type of storied campaign.