The cost is as likely to be the residual predicate on the quotation table. Try this small mod:

SELECT@F = COALESCE(@From, Min(QuotationDate)),

@T = COALESCE(@To , Max(QuotationDate))

FROMdbo.Quotation;

SELECT QU.QuotationId,

ISNULL(QUIC.Next_Follow_Up, 0)

FROM dbo.Quotation QU

OUTER APPLY (

SELECT TOP 1 Next_Follow_Up

FROM Quotation.Follow_Up f

WHERE f.Quotation_Id = QU.QuotationId

ORDER BY Id DESC

) QUIC

WHERE (QU.QuotationDate > @F OR QUIC.Next_Follow_Up > 0)

AND QU.QuotationDate <= @T

ORDER BY QU.QuotationId DESC;

WITH QU_Memo(Quotation_Id, R, Next_Follow_Up) AS (

SELECT Quotation_Id,

ROW_NUMBER() OVER (PARTITION BY Quotation_Id ORDER BY Id DESC),

Next_Follow_Up

FROM Quotation.Follow_Up

)

SELECT QU.QuotationId,

COALESCE(QUIC.Next_Follow_Up, 0)

FROM dbo.Quotation QU

LEFT OUTER JOIN (SELECT * FROM QU_Memo WHERE R = 1) QUIC ON QU.QuotationId = QUIC.Quotation_Id

--WHERE (QU.QuotationDate > @From OR COALESCE(QUIC.Next_Follow_Up, 0) > 0 )

--AND QU.QuotationDate <= @To

WHERE (QU.QuotationDate > @F OR COALESCE(QUIC.Next_Follow_Up, 0) > 0 )

AND QU.QuotationDate <= @T

ORDER BY QU.QuotationId DESC;