Windows 7 - [search] registry tool: snapshots, compare, re/undo.reg

Hi!

Ive been using a program called ARM - Active Registry Monitor ( time-limited trial version now available at Active Registry Monitor for Windows 9x/ME/NT/2000, the Windows Registry analyzer , formerly smartline vision) for a while, but since the program is
a) not free
b) in fact quite expensive (40$ for a comparably simple tool)
and c) not being developed anymore for years, it seems

... I am now looking for an alternative, preferably a free one.

Now, I know there are lots of registry scan / snapshot / installation monitor / uninstall / etc --- tools out there. I have tested quite a few of them, too.
But Im looking for some very specific features that so far, I could only find in ARM:

- take registry snapshots
- compare the snapshots
- export the differences between two snapshots into redo.reg and undo.reg

So .. if anyone out there happens to know a program that can do all of these things, and doesn't cost much (preferably: anything ) .. Id be eternally grateful.

Let me however stress this: I already have tested a bunch of programs that can do some of the things, such as taking snapshots, comparing, and exporting the changes in a file. So the important "rare" feature is the "undo" file.
Also please note that it absolutely HAS to be exportable in some way. I dont want the info stored in a way that only the registry-tool can handle, I want to end up with .reg files with as little work as possible.

Also, I get that its not terribly difficult to make your own "undo" file manually, from the "redo" file's info. It is however tedious and, in some cases, very time-consuming work. Not to mention that its frustrating to know that this could all be done with a single click, and that theres at least one program out there that can do it already

A tall order, I know.
Thanks in advance for all your suggestions