it will all depends on what you find once you strip all the underseal off, i have no doubt you will find some rot which might need welding, so unless you can weld the £200 isnt going to go very far if you have to pay someone to do it

i'd advise you to use new nuts & bolts, any fastner place will stock them and they wil cost pence, trying to clean up old nuts & bolts is a false economy IMO