anywhere between £700 -£1100. The usual places are front / rear arches, rear subframe, insides of sills ( rear mainly ) bottom of front wing, Rear doors. Front sub frame ( near chassis legs). When driving check for obvious smoke on hard acceleration, whining from diff ( although if none it will double the price

). It is better to get it already ply lined as it will save you £150 - 200. I can garuntee that others will add to this list but this is what i usually look for and havent had a bad one yet. Just make sure you get a good bit of MOT or a full one if paying more than £800- 900. Hope this helps.
marc.