Last Spring, I asked Lee Mac for a program to help me with my job at the time and he delivered. You can find the program here.
What it does is allow you to select various text objects whether they be DTEXT, MTEXT, Attributes… and then a simplified graphical calculator appears that lets you select a mathematical function (Add, Subtract, Multiply, Divide). then you select the next numerical text object and so on… When you are finished, you can place the total of the mathematical functions as a text object.
TC <enter> to start
The original source code can be found [here]. It is better to redirect you to the source code in case there are any updates, changes or improvements to the Lisp routine at Lee’s site, it is just easier to keep track of.