Pull First Date and Price

RobinOfSheffield 

I couldn't bring myself to type in all of those rows so I focused on the final six and came up with the following.

See if it gets you any closer to what you're after.

Staging the data

CREATE TABLE [dbo].[PurchaseHistory]
(
	[DateOfDelivery] [datetime] NOT NULL
	, [ItemID] [varchar](32) NOT NULL
	, [Vendor] [int] NOT NULL
	, [PurchasePrice] [float] NOT NULL
)
GO

INSERT INTO
	[dbo].[PurchaseHistory]
VALUES
	('2023-04-11', 'FX-1150-110', 5564100, 17.11)
	, ('2023-04-13', 'FX-1150-110', 5564100, 17.11)
	, ('2023-07-03', 'FX-1150-110', 5800500, 18.44)
	, ('2023-07-13', 'FX-1150-110', 5564100, 17.11)
	, ('2023-07-17', 'FX-1150-110', 5564100, 17.11)
	, ('2023-07-18', 'FX-1150-110', 5800500, 18.44)
GO

Example

Note: The LAG() function was introduced in SQL 2012, so if you're running an older edition (hopefully that isn't the case in this day and age), this example won't work.

SELECT
	 [data].[DateOfDelivery]
	 , [data].[ItemID]
	 , [data].[Vendor]
	 , [data].[PurchasePrice]
FROM
(
	SELECT
		ph.DateOfDelivery
		, ph.ItemID
		, ph.Vendor
		, ph.PurchasePrice
		, CASE
			WHEN
				LAG(ph.PurchasePrice, 1) OVER
				(
					PARTITION BY
						ph.ItemID
					ORDER BY
						ph.DateOfDelivery
				) = ph.PurchasePrice
			THEN 0
			ELSE 1
		END AS [Include]
	FROM
		PurchaseHistory AS ph
) AS [data]
WHERE
	[data].[Include] = 1;

Output

Cheers,

Lain