You are ahead of the game if you found a real nice car for $7K. But $7K cars usually need a lot of metal work. Much of the damage might be hidden. If you can perform the metal work yourself, then you are ahead of the game once again. If you cannot weld and fabricate, the repair costs will add up quickly. After you have a sound foundation, parts cost adds up quick--especially when temptation kicks in. Once that happens (tempation), it's very easy to talk yourself out of $50K.
And we, as a group, are a VERY bad influence.