Depends on how much variation there is in the expressions you want to
evaluate--and how much time you want to put in to make it work.
This is a User Defined Function (UDF) that has no validity checks. It accepts
exactly 3 cells and evaluates something that looks like =xxx(yy,zz):
Option Explicit
Function myFunct(rng1 As Range, rng2 As Range, rng3 As Range) As Variant
Dim myVal As Variant
myVal = Application.Caller.Parent.Evaluate _
(rng1.Value & "(" & rng2.Value & "," & rng3.Value & ")")
myFunct = myVal
End Function
If you're new to macros:
Debra Dalgleish has some notes how to implement macros here:
http://www.contextures.com/xlvba01.html
David McRitchie has an intro to macros:
http://www.mvps.org/dmcritchie/excel/getstarted.htm
Ron de Bruin's intro to macros:
http://www.rondebruin.nl/code.htm
(General, Regular and Standard modules all describe the same thing.)