Ten Value-Adding Questions to ask before finalizing your  Scope of Work:
1) Although ‘ in the budget' do we REALLY need it ?
2) Are all the included criteria / features needed ?
3) Can we ‘reduce' the required Sow (less numbers, less weight, less features etc... ) ?
4) Are there ( more economical) ‘ alternatives' that can ( almost ) serve the same purpose ?
5) Did we include too many ‘proprietary' features that may reduce competition and increase the cost ?
6) Did we consider ‘ the whole life cost' (as opposed to least expensive) of the major components of the intended SoW ?
7) Did we calculate ‘ the Value for Money' (as opposed to least expensive) of the major components of the intended SoW ?
8) Do we have existing contracts that we can re-negotiate in order to include / accommodate the intended SoW ? ( will save on the bidding process as well as mobilization and other costs)
9) Can we combine the intended SoW with other existing or planned contracts?
10) Did we review our data base of ‘Lessons Learned' to benefit from previous ‘successes' and avoid previous ‘ mishaps' ?

Your Scope of Work - SoW- ( or part of it) includes a service / product that is available from just the ‘one source'. Efforts to negotiate better terms (including more reasonable price) with the provider fail.
Here are some suggestions as to how to deal with the situation:
A)     Short to medium term   choices:

•  ‘Reluctantly and temporarily‘ go with the deal, possibly until you figure out a longer-term solution.
•  Negotiate a Long Term Price Agreement ( you may get better terms if you commit for a longer period)
•  Scrap / replace the service / product in the SoW.. whenever possible !
•  Go for a ‘substitute' ( similar not identical).
•  Use an alternative service / product that may (somewhat) achieve the purpose.
•  Amend some features of the service / product in order to remove the ‘proprietary' aspects.
•  Approach other suppliers for suggestions.
•  Approach other suppliers outside the ‘Monopoly' area (including possibly the original supplier of the service/product)
•  Combination of two or more of the above.

•B)      Longer-term choices:

•  Explore possibilities for a Barter (scratch my back, I'll scratch yours) . The supplier may need some of your products /services and therefore may show some flexibility.
•  Explore possibilities of ‘ Who knows whom' in your / supplier organizations. Personal relationship (especially at the Top) may work miracles!!
• Redesign your Sow to :
• a. Exclude the subject service / product
• b. Use an alternative service/product
• c. Include an ‘in-house' product/service (available within your organization)

FINAL NOTES: 

• 1) If you invest enough time and attention in preparing your SoW , you should be able to avoid including any ‘proprietary' service / product that may lead to a ‘Sole Source' situation.
• 2) When awarding a contract special care should be given to avoid putting ourselves in a ‘Monopoly' situation ( such as availability of ‘maintenance' services and spare parts exclusively from the OEM)