Build a custom pricing tool for shopify

General information for the business: Well sell window blinds on-line
Kind of development: New program from scratch
Description of every module: We are looking at utilising either shopify or bigcommerce as a webshop.
None seem to provide pricing options for a custom made products.

we need to price based on width and height.
currently we use a table or matrix/array to price this
Description of requirements/functionality: Enter Width (between 0 and 3000)
Enter Height (between 0 and 3000)
Enter Fabric Type

Return price and have this price work with the Shopify webshop.
Specific technologies required: Java Script in Shopify /Bigcommerce
Extra notes: Need to clarify

refer to existing website:
www.iseekblinds.com.au and pricing