Strength bows are those described on DMG 64 under the “Strength Bonus Considerations” section.

Is is recommended that if strength bows are made available, they have at least one downside other than cost. If the cost is the only downside, it provides a way to purchase a considerable power upgrade at a store, which is basically unprecedented in the game. Perhaps make them require maintenance like the UA plate armor,¹⁾ or obtainable only through questing.