GPS based tracker for cat

Hi, I am looking to build a GPS-based tracker to keep track of cat. Specifications for the device: --It needs to be lightweight. (It has to sit on my cat's collar. The cat weighs about 8 pounds) --The device will be used outdoors and has to have a tracking radius of just about 3 blocks around the house. --It doesn't have to offer constant updates but I should be able to check it every hour or so to note the location of the cat. I would love to hear any suggestions on how I can get started and what I should be looking at. Thanks all!

Check out the Garmin Rhino series, 2 way radio with integrated GPS

 Might be a little big, but I have seen people put them on their dog so they could find them in the woods.