MultiTracks come in two file formats, WAV and M4A. Though prices can vary, the WAV file is typically $39 and the M4A is $35 per song.
CustomMix also comes in the same two file formats. The WAV file is $15 and the M4A file is $12 per song.
You can find the prices next to the file type on any song page whether you're in MultiTrack preview or CustomMix preview.