My organisation is a consultancy, and we have a number of different "rate sheets" which we use to price jobs. 

We record in Salesforce which rate sheet applies to each Opportunity.

We also record in Salesforce the projected margin which we expect to make on the Opportunity if we win it.

For each different rate sheet, we have estimated what a typical/average margin would be.

What I'd like to do is this.  When an Opportunity is created, the margin will be set automatically within Salesforce as a function of the rate sheet which has been selected.  But then the user can over-write the margin - typically, when the bid is submitted - with a number that has been calculated specifdically relating to that Opportunity.

I know I can use the CASE statement in a Custom Formula field, but I don't think that can be made editable.

I know I can create default values for Custom Fields, and I know that the default value can be calculated using a formula, but I don't think the formula can refer to other Opportunity fields.

Have I overlooked something?
Thanks in advance for your help.

My organisation is a consultancy, and we have a number of different "rate sheets" which we use to price jobs. 

We record in Salesforce which rate sheet applies to each Opportunity.

We also record in Salesforce the projected margin which we expect to make on the Opportunity if we win it.

For each different rate sheet, we have estimated what a typical/average margin would be.

What I'd like to do is this.  When an Opportunity is created, the margin will be set automatically within Salesforce as a function of the rate sheet which has been selected.  But then the user can over-write the margin - typically, when the bid is submitted - with a number that has been calculated specifdically relating to that Opportunity.

I know I can use the CASE statement in a Custom Formula field, but I don't think that can be made editable.

I know I can create default values for Custom Fields, and I know that the default value can be calculated using a formula, but I don't think the formula can refer to other Opportunity fields.

Have I overlooked something?
Thanks in advance for your help.