NEC3 using different subcontractor quotations to add / omit works

NEC3 Option A, Contractor has submitted a quotation for a change to the Works Information. The change includes for additional work and some work to be removed. The Contractor has gone out for three quotations and has used the highest sub-contractors quotation for the additional works. The Contractor is also using the least expensive quotation to omit works not going ahead.

Should the Contractor be using the least expensive (value for money) quotation for the additional works, providing the subcontractor complies with all contractual requirements (SSCC + fee & subcontractor fee %). How do I deal with the omission of works - the Contractor priced for the tender?