Yea mate, you might get lucky with someone selling one new for around that though, but seriously, if you're willing to spend £600 on coilovers £600 on a diff is well worth it, it made the biggest difference in handling to my car out of all the mods I've done to it. (I got lucky and got a box with one fitted for £150 unknown to the previous owner!) Just gives you a new level of confidence in the cornering ability of your car, but you would want to get the right diff to suit your driving style though