Vix...my organization has been using a figure of about £50-60K but I would too be interested to know how they came to this. I am new to this organization and have asked the same question.

The most understandable will be to cost your participating bid committee members like at consultant rates.
1. Bid Specification Committee members. [BSC]
2. Bid Evaluation Commitee members [BEC]
3. Bid Adjudication Committee members. [BAC]
4. SCM Practitioners including secretariat and administation support personnel.

The costing model must include all expenses [labour; travel; accommodation; meeting venues; catering for meetings; computer equipments and data projector; voice recorder for minutes and stationery / consumables]. Note that BAC meet first during the approval of Tender Specifications and second during the tender adjudication.

Regards'
Cecil
South Africa