I was in the same boat as you until I stumbled on a real, money-saving project. My PetSafe invisible fence wired transmitter blew out, and I wasn't keen on dropping over $100 on a new one. After dragging my feet for a few weeks and doing nothing about it, I realized that I could probably replicate whatever the transmitter was doing with my RPi. Sure enough, somebody online had hooked their transmitter up to an oscilloscope and figured out the correct signal pattern to send over the wire. If I have time tonight, I'm going to finish the code and test it out. When I'm done, I should have a new transmitter that I can control via my phone for significantly less money than the junk PetSafe sells.