If you are budget minded I would like at test-pipes and keep the OEM rear. Will give a nice volume increase and even further exemplify the higher pitch euro race sound vs. american muscle/nascar. Depending on which sound you like, both options can be had for 500-600 dollars. With the test pipes you get 20whp extra to boot which is hard to pass up.
Test pipes/catless with a megan I would image to be just obnoxiously loud