Help Creating a UDF for fees

[Cartopia]

Hello, I need help Creating a UDF that calculate buyer fees when looking at wholesale cars to purchase. I have an algorithm that I created to know how much I want to bid at IAA Auctions which is a insurance salvage auction. They have a very simple fee structure and it could be created with an "If / Than" function, I tried to look on you tube to help create a UDF but the creater used such technical jargon that I got lost. I have included the PDF of the fees associated.

 

[Cartopia]

IAA Buyer Fees PDF

If anyone can help me develop a UDF, the page that is most applicable is the 1st page as I am a licensed dealer, the UDF should include the buyer fee as well as the internet proxy fee. Also can someone point me to a easier and more understandable tutorial on how to create a UDF, I am by no means an expert at excel, but I'm a quick learner. Thank you in advance for you help with this.