Simple calculator type program needed

Very simple program needed. I have the file loaded in excel that we use to determine what kind of value we give to a customer for a trade in phone. The program will let us put in a phone model name e.g. "Nokia 2125" from a drop down menu or list of some sort. Then it will let us choose fair, good, new condition from another drop down menu which will then give us the price for the phone. We have a percentage that goes off by the retail price of the phone which is saved in the excel file attached in this post. This is a very easy program (like a calculator in way) that will take some of you minutes. I'm always on guruDOTcom but rite now there site is down for some reason so I had to come here and use this site. Hopefully I can find some one willing to make this for me asap. I'm going to offer $100 or more. We sell phones in our stores and sometimes a customer comes in with a (old, fair, new phone) that we use to give them a trade in value. Say you're buying a 200.00 phone and you give us a fair motorola phone. We'll give you $15 for it. We have an equation set up in excel that makes sense and all you would have to do is have a calculator that i can chose the phone model (select from list)(or some sort of drop down menu) and then the condition and the calculator would give a trade in value for that phone. I am attaching a quick draft i made in paint to what i want it to look like and also the excel document explaining everything.