Wow. That's really a shame that you had to spend so much money and jump through so many hoops to end up with a reader that doesn't work for you.
Don't deregister your Kindle. There are certain perks that come with a registered Kindle, like the ability to use the @free.kindle.com auto-conversion service for certain file formats that will make them readable on the device.
I suggest that since Amazon won't officially allow someone from your country to buy books in their store, you familiarize yourself with alternative e-book sources, especially the ones which are DRM-free. You're in luck if you like sf/fantasy or romance genre fiction, which are readily available via Baen's
Webscription,
Fictionwise's MultiFormat listings, which are even cheaper with the discount coupons they've been putting out pretty frequently, and plenty of small romance e-bookstores, that will cheerfully sell to customers all over the world.
And maybe also learn to remove DRM and convert files to sideload onto your Kindle, because no other e-bookstore which sells its books as "Secure" DRM-restricted files will have a format that the Kindle will accept. Except for password-protected PDFs, which you can now use on the K3. We can't really discuss how to do this in detail on the forums, since it's a legal grey area in certain countries, but the information is readily available online.
As for getting the books onto your Kindle, you do not need to email them, or use PDF, though you're certainly welcome to do so if you like.
Just hook up your Kindle to the computer via the USB cable, and drag and drop the files into the "documents" folder. They will need to be in PDF, .mobi/.prc/.azw, or .txt. The Kindle will not reject your books, although it won't see them if they're not in a compatible format.
You can use the free application Calibre, which has its own subforum here, to convert any non-DRM copy-restricted book. And you might as well get your money's worth out of Amazon's auto-conversion service, which will handle .doc, .html, and .pdf files (be sure to use the @free.kindle.com address, the regular @kindle.com one comes with fees).
If you master the necessary DRM-removal skills, you can also try the Philadelphia Free Library, which lets non-residents borrow their e-books for the cost of a $15 card per year. Perhaps see if
Kobo will let you shop there. Sign up for an account and see if they let you download one of the Free eBooks from the link at the top of the page. They're supposed to be very good about international customers, though it may make a difference that you're in Zimbabwe instead of, say, Sweden.
There are plenty of good sources for legal free e-books, including our library of public domain classics hand-formatted by our members right here. Just click on the E-Books tab in the blue navbar at the top of the forum to see the listings.
There's also the public domain archives of both classic and obscure out-of-copyright works over at Project Gutenberg and its spinoff projects, Feedbooks and Smashwords carry a lot of free self-published stuff, which is admittedly of varying quality, and plenty of established authors and publishers put free short stories and even entire books for download on their websites.
Alternatively, if you really want to buy books via Amazon, you could always set up a US-address account and use a US-based IP-hiding VPN proxy so that Amazon easily can't tell you're in Zimbabwe while buying stuff. Plenty of people do this in order to purchase books that simply aren't available in their area due to geo-restrictions.
Hope this helps, and welcome to MobileRead!