I don't think you're going to add any speed to your 300C for $1000. If you want to improve the sound, you have a few options. I'd start by looking for a complete take-off factory dual exhaust from a 300C or a Charger R/T. You should be able to find something on Craigslist for $100-200 or so. Another $100 or $150 to install it, and you've have a deeper exhaust tone with just a little bit of rumble to it, and something like an 8 HP increase, which is a hell of a bargain for the money. If you really want to capitalize on it, buy a tuner like a Diablosport. That's about it. It's very easy to spend a ton of money modding a 3.6 and still wind up nowhere near what you'd have in a 5.7 for roughly the same cost difference, plus you'll still have the puny BR3 brakes and other suspension parts.
If that $1000 is just burning a hole in your pocket, contact Solo Performance and see if they make a catback for your car. I know they have them for the V-6 Chargers, but I'm not 100% sure they have one for your car, you may have to swap your stock tips over. That won't give you any more power above what you'd get from an R/T exhaust, but it would give you the best sound you can possibly get on a 3.6 without drone.