Curious pattern of data loss in Win XP

I noticed yestereday that many of my personal files were seemingly randomly deleted on my home PC. The pattern is a bit odd, so I'll explain it as I saw it. I don't know anything about viruses or hackers, so I can't even begin to guess how this happened - I just know that I didn't directly delete these files.

So far, the only date I've noticed I've lost was all contained within My Documents.

1) ALL of my digital photographs! Thousands. I had them saved within My Pictures, organized through Picasa (a photo manager program, akin to iPhoto). The My Pictures folder itself was not deleted. Only all of the sub-folders that I had my pictures organized within. Curiously, the few scattered photo files I saved within the My Pictures folder directly (hence, not organized in any of these many sub-folders) were not deleted!?

2) I had a folder called "Writings" in which I saved many word documents I had created. Again, the same scenario - sub-folders ALL gone, but the few documents in the root directory unaffected. Note that my great bulk of word documents, saved within My Documents itself, were uneffected.

3) A 1/3 of my iTunes music - and very specifically, everything after U! iTunes organized all of the bands alphabetically in subfolders throughout My Music, and every band after the letter U has disappeared. No other band from any letter before U lost a single song.

This is curious, frustrating, and frightening. It seems like this sort of thing is very personal and deliberate - as if someone directly deleted the files from my computer. Can this be a pattern of a virus - my updated scanner detected nothing.

I have been able to find these files usinga data recovery program, but many are lost forever, and the data program that I used to find them now wants me to pay $100 to buy "credits" towards reclaiming the nearly 7 GB of data I lost? ANY suggestions on free, or at least cheaper, data recovery programs, where I could easily recover thousands of files? They are still there, or at least a lot of them are.

I'm running the most fully updated version of Windows XP Pro with their standard firewall.