If proposal cost is increasing high - how to reduce it?

Reduce the quantity through value management.

the question it self is unclear any how a value engineering process should be part of design discipline from early design stage

try to use better idea and your experience for alternatives with out reducing quality  

I accept with the said answer. 'Value Engineering' is the key.

If Value Engineering is allowed, this will be the1st solution, if not then either by finding alternative sources/ suppliers with lowers prices, reducing the indirect cost, reducing the overhead fees.

Value engineering is definitely the first option but also need to work on Man power planning by optimizing the resources and using the best available talents.

Optimize your design. Plan it carefully by using good design softwares. Use alternative design procedures like ASD, LRFD and if possible use Plastic design for steel structures if the client is okay with it.

Re-check the design margins and utilize the full strength of structure and optimize the quantities. 

Structural Engineers can tell you if it is possible to reduce proposal costs.

Review first the project plans and quantities based on Program of Works, And shop drawings then colect and select to minimized/ Adjust the bill of material's used and re-design/ re-construct the project proposal, if needed

There are many areas from where we can control and reduce the cost.

1- Micro programming to identify the cost reducing points.

2- Better programming which contain cost reducing data.

3- Try to control stoppages or delays, which normally comes in normal practices.

4- Use of GMP or best operational techniques.

5- Reducing of workable time to save Labour and energy costs.

6- Availability of Labour and equipments on time.

7- Try to use modern techniques and machinery.

8- Use of continual improvement.

but remeber not to compromise on quality and standards commited to a client.

Thanks