Some newer releases offer three or four buy options instead of one, for example a standard bonus, a super bonus with more scatters, and an enhanced version with guaranteed multipliers. Each tier has its own price and, more importantly, its own RTP. The tier comparisons I found at https://thebonusbuyslots.com made it clear that the cheapest option is not always the worst value per dollar spent. Higher tiers just concentrate the risk into one very expensive spin.