Create dynamic spec and pricing engine

I am looking to create a dynamic web site which will allow the user to select from 24 product categories, then change 5-10 variables within each of those product categories, and then automatically calculate a price based on these variables. There will also be some logic within the 5-10 variables (e.g., if you select option A, then Option B will have ABC drop-down. If you select Option A1, then Option B will have XYZ drop-down). All this logic will be fully documented. There are a couple web sites out there which do something very similar to what I am trying to build. Those interested in bidding can send me additional questions and I can send you further details on the sites that have similar functionality. Note that I have a preference of building this in .NET / SQL Server, but am relatively flexible here. Could also do PHP/MySQL if that is the coders' preference. Also note that this quote should just be for building the basic functionality. We will also want some design/UI help, but are focusing on the core functionality for now. That said, if you would like to help with the design/UI, happy to talk about adding that to the scope. Looking to complete this in the next week. Thank you, Pat