My side exit was around £40ish for the backbox, then a Japspeed de-cat, plus £90 labour and materials from Powerflow. So £130 plus whatever a Japspeed de-cat costs! So quite cheap in terms of exhaust systems!
Mine sounded nice, both on and off boost. Screamed very loud on boost though! When I had it and running 1Bar it made normal-ish BHP figures but seemed to produce lots of torque...not sure if the exhaust was the reason, but yeah, it was good but I fancied a normal rear exit exhaust so sold it! I got some pics if you want a looksee.