what the...?

Why do I feel like such a dummy today for not backing up my pc? I keep finding mp3s that I knowingly purchased digitally, mostly accompaniment tracks, then proceeded to put them on backup drives. Now, upon doing a search for some of them, they can't be found. The only thing I can think of is that possibly they were on one of my former puters who died. In the past 2 years I've gone thru 3 puters. This includes the one I'm currently using. SO of course now since I can't find the digital files, I've been having to re-purchase them. (Cha ching cha ching.) I'm not about to invest in one of those "online backup" sites unless it's free. I'm already paying for internet subscriptions, memberships, etc. I'm also trying to SAVE money. ;) Just had to voice my frustration over this! AAACK!!