At clause 62.1 the contract does permit the PM to instruct the contractor to submit alternative quotations. Before doing so though the PM is required to discuss different ways of dealing with the CE with the contractor.
If you and the PM can't find common ground on the method for preparing quotations there is a risk that when they are submitted the PM either rejects them and instructs you to submit a revised quotation, or worse still to make their own assessment if they think you haven't assessed it correctly. I wouldn't want to put the PM in the position of making their own assessment so I'd suggest rolling your sleeves up an splitting into three quotations as best you can. If it is impossible to do this maybe explain the difficulties your having to the PM and you may be able to convince them to allow the submission of one quotation. Both parties need to remember that the contract merely requires us to "assess" CEs, often we put too much focus on trying to "calculate" them precisely!
If you and the PM can't find common ground on the method for preparing quotations there is a risk that when they are submitted the PM either rejects them and instructs you to submit a revised quotation, or worse still to make their own assessment if they think you haven't assessed it correctly. I wouldn't want to put the PM in the position of making their own assessment so I'd suggest rolling your sleeves up an splitting into three quotations as best you can. If it is impossible to do this maybe explain the difficulties your having to the PM and you may be able to convince them to allow the submission of one quotation. Both parties need to remember that the contract merely requires us to "assess" CEs, often we put too much focus on trying to "calculate" them precisely!