As suggested, you can buy a junk board, or any piece of electronics that will have parts and trash it to use the boards to practice.
However, the kits that I am suggesting you can use to practice on range in price. Jameco classifies them as 'educational and hobby kits'. You can make anything from cute little LED decorations with or without timing circuits, or you could build a radio or an amplifier, or you could build miniature robots. You may very well choose not to go this route, but I am going to toss it into this thread as it may help someone searching this subject in the future.
Again, just a really good way to practice board work, and and perhaps if you do it right, gain a great sense of accomplishment if you do it right. Yes of course you could mess it up and be out $15-$20 bucks, but that is a heck of a lot cheaper than ruining or doing more expensive damage to a card.
Here are some examples of cheap kits:
And one not so cheap ($35), but cool and actually useful:
There are all sorts of kits out there.
The other plus of building one of these kits is that all the electronic components come loose, so that if you really want to learn electronic repair, as you go along, you might want to look up what a particular component is and it's function. Electronic repair is not simply about desoldering out a part, getting a replacement, and putting in the new one. Sure there are many applications where this is all a fix will be, but having a basic understanding of the component you are dealing with will be very helpful, and could easily save you lots of headache in the future.