Hey Mike Obrzut,

Thanks for getting in touch,

You dont need to purchase anything to convert files.
This process can be done inside iTunes.

1. Launch iTunes.
2. Navigate to "itunes preferences"
3. It will load up a window, click the GENERAL tab
4. Click "IMPORT SETTINGS"
5. Import Settings set to "MP3 Encoder"
6. For setting click CUSTOM.
-- Stereo Bit Rate: 320KBPS
-- Sample Rate: Auto
-- Channels: Auto
-- Stereo Mode: Joint Stereo
-- Leave other boxes UNTICKED.
-- Click OK.
-- Close the preference window.
7. Find the MP4 / WMA file in your iTunes library.
8. Rightclick on the file and select "create MP3 version"

Once the encoding process has been completed.
Navigate to MUSIC/iTUNES/iTunes Media/Automatically Add to itunes

Inside this folder you will find the new MP3 versions you have made.
Move these files into SERATO DJ.

Let me know how you get on :)

Thanks!