In the UK my ISP (which has excellent service but a small customer base, so it has actual quotas, not a faux "unlimited" service with some hidden usage policies) charges £45 pcm for the cheapest 200GB quota and £55 pcm for 2TB quota. So that means 1.8TB of quota comes to £10 pcm end user cost (ie that has their profit and taxes baked in). Maybe much less difference than you realised.
In the UK my ISP (which has excellent service but a small customer base, so it has actual quotas, not a faux "unlimited" service with some hidden usage policies) charges £45 pcm for the cheapest 200GB quota and £55 pcm for 2TB quota. So that means 1.8TB of quota comes to £10 pcm end user cost (ie that has their profit and taxes baked in). Maybe much less difference than you realised.