Spend some of your budget on making the mounting for your kit as stable and safe as you can. For example, I use a tripod and tape it to the ground with strong tape, or stake it down with tent pegs if it's outside. If you use a power adapter, tape the cable down too.
Don't worry about stopping the timelapse at night - just discard the dark frames when you're post-processing.
For a three month timelapse you're going to need to clean dust from the lens a few times without moving the camera. Make sure the front of the camera is accessible (eg not right up against a window), and the mounting is secure enough to stay in place while you do it.
Check that the sun isn't going to shine directly into the lens as the sun position changes over the period. Direct sunlight focussed onto the CCD for a few hours will kill the camera.
Finally, you could probably increase your framerate - with a 1 hour period, each frame will have the sunlight coming from a different direction, so when you put it together at the end you'll have a strobe effect. If you can shorten it to 5 minutes you'll get smoother lighting transitions - you'll see the shadows swing around and the clouds traverse the sky as the day passes.