There are some that put on a straight chrome tip for about $50. Most of us went the full route and bout the R/T valance and installed dual exhaust. Depending on how sophisticated you go, it can cost you $250 for a shop to make a Y for you, $500 for a Blastin Bobs Y pipe or $1k for Magnaflow cat back with a Y and dual exhaust. That is what I did.
If you are looking to just add one of the tips to the single exhaust, it isn't a quick bolt-on. The rounded tip on the single exhaust is a welded piece of the rear resonator. You would have to cut that off and either weld one of the ball socket-type ends from a donor dual exhaust to the resonator and then bolt it on or somehow cut the rounded tip and try to kludge something to get the tip to bolt on. You would need to cut your stock rear valance to make the new tip fit.
If you are looking to go dual exhaust, it can be done pretty inexpensively. A lot of R/T guys are selling their take off exhaust cheap. I have even seen people giving them away. Here is a great write-up of how to do it. Just be prepared with the things you will need in addition to the take off exhaust.
New dual exhaust valance (or you can cut your current one)
heat shield for the driver's side (I suggest you get the sticky back stuff from Summit)
2 J-bolts hangers for the drivers side back by the resonator
2 rubber hanger grommets
2 rear clamps exhaust tip clamps if your take off exhaust didn't come with the tips attached
Here is a picture of mine with the Mopar quad/split tips.
I went with a take off from an R/T automatic. It added a little sound (maybe a little less than I had hoped), no change to performance (not that I had any expectations), but I love the look (which was my primary reason for doing it).