Evaluating a text field as a formula

Hello World!!

I've been racking my head here lately wondering if this is possible and I'm hoping that someone can tell me it is and how to do it.

Ok here's what I'm trying to do:

I'm trying to create a form that will

1) create new inputs that I call estimates in a table called Estimates

     Definition of table:

     Estimate_ID

     Estimate_Name

     Estimate_Description

     Estimate_formula -- (user defined formula to calucate the estimate)

2) Create multiple inputs per estimate and have these inputs will be stored in a Estimate_Inputs table..(estimate_id will be the key between the two tables)

    Definition of table:

     Estimate_ID

     Input_ID

     Input_name

     Input_type -- (constant, %, etc)

     Input_value -- (user defined)

My end goal is to create a way to store values for a formula in a table and extract them when needed to execute a given formula as defined in Estimates:Estimate_Formula field of another table.

ex. 

     Estimate table:

     Estimate_formula - "= Level_of_Effort - SUNK"

     Estimate_Inputs:

     Input_Name - "Level_of_Effort" |  Input_value - 25000

     Input_Name - "SUNK" |  Input_value - 1000

     Answer: 24000 =        25000        -   1000

                              "Level_of_Effort" - "SUNK"