Paste the purchase history you already keep. Each row becomes a delivery with its own price, and the purchase is posted to the ledger at the same time.
A header row and four columns. Everything else is optional, and any column that is not one of these is ignored rather than rejected.
Tab, comma and semicolon separators are all read — pasting straight out of Excel works, and so does a file exported on a machine that uses the comma as a decimal mark.
Nothing is written until you have seen every row and pressed import. If one row is wrong, none of them are imported — a half-imported set of books is worse than none.