If you want to stick with the OEM look, get GFX tips and call it a day. Only $30 to $50 bucks depending on where you get them from. Hell I'll sell you mine for $30 if you'd be willing to cover shipping from Canada.
The GFX tips go on just like the OEM ones, which are screw-on I believe. They are also angle-cut so that they flow with the rounded bumper better than the OEM tips. Whether you weld, screw, or clamp them on, you won't be able to tell once its done since the muffler tip will sit far enough into the bumper. I'd say go the screw-on or clamp-on route since neither are permanent.
If you want something aftermarket, get the M2 exhaust on eBay, bolt it on and you're done.