It would be particularly useful to be able to mark up pricing tiers by percentages, even better if positive and negative. i.e. rather than selling a $6 cost product for $9, you select you want a 50% markup by typing in.
Perhaps try discount rules - you can create rules to give % Discounts, then assign these rules to certain customers and or products.
What I would find excellent is to create a price level that mark-up up products by % of average cost.
Retail price as a percentage markup above average cost would be beneficial
This would make life a LOAD easier and margins more accurate as they will be live, not waiting for a price update by the user once a month or quarter, etc.