Test Pipes will be the cheapest option, but they will require you to cut out the OEM Cats (which means if you ever plan to sell it in the future, unless you sell to an enthusiasts you'll have a problem).
Buying just an X-Pipe (Mastermind, Challenge, Fabspeed) is probably your best option combined with the OEM Axle-Back section. You'll get all the HP gains of going catless (or HFCs), without being obnoxiously loud (majority of the noise is from swapping your mufflers out).
The Akra is an incredibly quality piece, but it's gonna run you ~$6k brand new (which isn't exactly budget). Meanwhile the Test Pipes are ~$500 and the X-Pipes I listed go from $1.4k-$2k.