Dear all, please help me if you can...

I'm running a G5 / 2.5 Dual Processor under Mac OS 10.3.8, and I recently lost data.
In fact, I can't remember erasing it, but I assume I did it cause I can't find the files.
I'm talking about 1.50Gb. I may have erased the folder that contained it all. But it's strange cause it was important data to me, and I dont think I would erase it by mistake.
Can data disappear because of some disc fault or something?

Anyway, let's get to the point.
As I haven't writen anything after I noticed that they had disappeared (on the partition the files were in), I tried to recover them using Techtool Pro 4.3.
The result of my attempt was a 4.61Gb file called 2Z694-5064.dmg.
But when I double-click it, I get a window saying: "The following disk image failed to mount. Reason: No mountable file systems."
Unfortunatelly I'm bot surprised, as I've been told that Techtool is just as good as Norton's bull shit.

So then I contacted a few companies in the UK who specialize in recovering data.
But they charge a lot of money! And although the data is important, it's not worth what they charge.
Having said that I'd still like to get it, and I've been reluctunt to use that 70Gb partition while I'm not totally convinced that there's no cheap way around it.

I've also been told that the fact that Mac OS 10 is based on Linux makes it very hard to recover deleted files... I have no idea why...

Is there antone who could help...?