DECLARE @c TABLE ( a INT)

INSERT INTO @c
VALUES
(22999),
(23004),
(23005),
(30000),
(45000),
(58000)

DECLARE @P TABLE ( a INT)

INSERT INTO @p
VALUES
(23000),
(30000),
(45000),
(58000)

SELECT 
*
FROM @P p
OUTER APPLY
(
	SELECT TOP 1 c
	FROM 	
	(
		SELECT MIN(a) as c
		FROM @C  
		WHERE  a >= p.a
		UNION ALL
		SELECT MAX(a) as c
		FROM @C  
		WHERE  a <= p.a
	) c
	WHERE c.c IS NOT NULL
	ORDER BY p.a - c.c DESC
) x