Microsoft Excel Activation

We need Microsoft Excel for our home business. We do not need anything else but Excel. I have found the standalone program for sale for around $65. I see reading the details it can only be installed on one computer. Which is fine because we only needed on one computer. What I am wondering is what happens when I replace the computer or something. Am I not going to be able to reinstall the program? I am wondering if I would be better off paying the money to get the whole Microsoft office program that I can install three times. I just hate to spend the money to buy programs that I do not need. I am looking forward to your advice.