if you stick mot history in google youl find the dvla site where you can check its mot history... will every mot failure and the reasons. you only need the reg no.
most welding is done after a mot failure, so no welding on history is a good indication
if its clean maybe 2k if youre really desperate to have it. 5 is ridiculous youd be better off buying a dog and having it done then youd know what had been done.