Best bang for buck is a tuner. If its gonna be your daily driver, then I would get the tuner and call it a day. But it really boils down to your definition of what ''terribly expensive'' means.
There are a lot of mods you can do for a reasonable amount of money, but none in that price range will alter the truck as much as a tuner. Ive been though this with many trucks. One of my current vehicles is a 2012 RT. I started my modding journey by adding every bolt on available to it. And unless you are modding it just for your pleasure, I would stop with the tuner.
This is simply my advice based upon my own personal experience on the subject.
I wish you luck no matter what you decide. I hope you continue to enjoy your truck. Im still as happy with mine as i was the day I drove it off the lot.