They are the primary ones that you should do before anything else and they are just about the cheapest too. For my CAI, all I did was buy a K&N High-Flow Filter that was shaped like my stock filter. It cost about $40.00 at AutoZone. The K&N Filter is cleanable and reusable so it saves you money over buying stock disposable filters. After cleaning the filter you have to treat it with K&N Filter Oil. The initial filter comes preoiled. I believe an extra can of K&N Filter Oil costs $10.00, but it lasts for a few cleanings.
My 180 Tstat I purchased is a Moto-Rad Fail-Safe Thermostat. That means when it goes bad, it will lock open so the water will still keep flowing. It cost me, $10.99 at AutoZone. When you replace the Tstat you need to replace the gasket. I believe, it will cost $2.00. I also had to install an additional paper gasket when I replaced my Tstat because I couldn't get a good seal when I put the Tstat Housing back on. Water was leaking slightly. I bought a generic sized paper gasket and had to cut it to fit properly. This cost another $1.00. That'* my story.