Tiered Pricing Calculator

I think I'm getting there.. but I'm still coming up short. I changed the last section to just the dollar amounts:

{15;10;6;4} and the number is almost correct, but it's over by about $30k. The marginal formula is going to charge the customer $15 for the entire qty, so let's say it's a quantity of 6k, all 6k will have $15 per item and then 1k-5k will be $10 per item, etc. I only need the first 1k items to be $15 each. I'm not sure this is the right formula?