Remove Duplicates - Challenge!

Hello All,

Having difficulties with a table. I need to reduce its size to increase performance by selectively removing duplicates. Ideally I would like to do this via PowerQuery. If I must a calculated table would work. Here is a sample of the data. What I am hoping to do is to remove each duplicate in the "Cost" column for each consecutive date for each item. In the table below I indicate the entries that should be removed. The table is currently 350,000 rows and I think it can be reduced to under 100,000. It feeds a complicated dax query that takes a long time to run against such a large table. Please advise.