pricing requirement

Dear Friends

I have a client requiurement , where user will decide the price value out of 4 values based on some external factors which are out of SAP application and he selects one price.

Let us say, a material price is around 100/200/300/400 and based on some factors , he had to choose among these 4 values only,say suppose he decided 200 rs.

How to go about this requirement.Pls suggest.

Thanks & Regards

Mahendar