Need a little advice about owing someone money. A couples questions.

Heres the situation. About 4 years ago I got into drugs and other BS. Naturally, as a dope fiend, I always needed money. I had lost a couple jobs I had and lost the apartment I was living at.

To make a long story short, I borrowed money from a family member, well to be exact, my god father. I forget what lie I made up but he lent me $200. But he stressed to make sure I pay him back. Not because he needs the money, but because of the principle. He is pretty well off.

Well here we are 4 years later, I am drug free and clean for 4 years now and I live in a different state. I havent talked to him since. But everytime I think about the money I owe him it makes me feel terrible and ashamed.

Here are my 2 questions:

Would it be acceptable to send him $100 now with a letter of apology, and explain my situation. And let him know I will pay the other 100 as soon as possible?

I would send him all $200 now but I am not working and had to save what I have now. So I dont have the $200.

Would it be offensive to send half now? I can recall owing people money in the past and trying to repay part of it and they get all pissed off and say "just keep it and pay me when you have the full amount". wtf

My second question is: is a cashiers check or money order the safest route to send in the mail?

Thanks in advance GLP!