i was really into the trashy punk thing a few years ago and looked into them, trying a few out.
would absolutely agree with felines comments. its cool to have a trashy vintage axe, but are you getting the best guitar for your money? i found them quite heavy to lift.
some people like the "salt'n'pepper" pickups in these models. i didn't try them through my rig, so not really possible to say.
i would rather spend my money something else - maybe an RD series, or a Les Paul Studio with MIII switching, or a swamp ash studio... if i wanted an unusual gibson.
pay maximum £400 probably, unless its a truly amazing one. interest in these guitars for grunge/punk has pushed the prices to almost unrealistic levels IMHO.
edit: on the models i tried - the pickups weren't "Dirty Fingers", but "Salt'n'Pepper". If they really are Dirty Fingers, its worth paying a bit extra.. i'm fairly sure dirty fingers weren't fitted to sonex 180s, but i might be wrong and they were fitted to some later high-end models.