Retail pricing calculator

Hi, I am trying to simplify my pricing process for 80,000 products we sell on ebay.

I want a formula based on the net cost price to calculate the Sell price (BIN) the area some fixed costs
(fixed fee and postage) but there are also variable fees which are calculated as a percentage of the selling/BIN price. So my problem is how can i create a formula that will calculate a selling price that returns a net profit for any price break of a set criteria of say 10% or £2 per item or slightly more complex a profit of 10% with a maximum of £2 and maximum of £3.50.

I want this to be a formula statement that i can paste directly in to my eBay listing software (Channel Advisor) which can calculate the selling price based on the cost price that it knows and the fees which I have explained.

see my example sheet LP prices Marr 22 page and the criteria page are the most important