Average total cost on a tiered pricing table

[Littleowl]

Hi All, hope you can help me

Can you please help with the formulas to find the average total cost a client will pay if they purchase initially let's say 13,000 and then also if this quantity increases/decreases along the way?

Tier 1: from 1 to 5,999 at $10.50
Tier 2: from 6,000 to 7,999 at $10.00
Tier 3: from 8,000 to 9,999 at $9.50
Tier 4: from 10,000 to 12,499 at $9.00
Tier 5: from 12,500 to 14,999 at $8.50
Tier 6: from 15,000 to 19,999 at $8.00
Tier 7: from 20,000 or above at $7.50


Thanks.