What do you think about inserting affiliate link into free desktop app

Hi
I have small desktop music application that is downloaded few hundred times each month

Its small utility that handles mp3 files, I wander what is the best model to get some kind of revenue out of freeware application , does making pro version is the only way ?

Do you think its good idea? Some one has experience with such thing?

Why only limit it to Amazon? If it handles mp3 files, you could also include other sources for music or audio books.

Just give it a try for a month or three. Than you will know, if it is a good idea.
Keep an eye on tracking the results, how many downloads with the new affiliate link to amazon and the period where you have given that version away.

You may also think about making the "Affiliated"-Version the main one and a Version without it to be downloaded for a small fee. You will than see, what your customers prefer.

Hope this helps.

Get it to 100x more monthly downloads first, then you can start experimenting with ads, affiliates, donations, etc. and make some real money.

By the way, one good place to ask for donations is the update download page, linked to from the "New Version Available" pop-up, assuming you have one.