When heads blow, people usually junk the car because it is an expensive, major fix. Most people would give the car away for free. Also, there has to be a reason why the head gasket blew. There could be a slew of underlying problems that caused the engine to overheat and blow the gasket that have not been fixed. On top of everything BMW parts are not cheap or easy to come by. A new BMW may be a status symbol but an old BMW is a heap of junk. Walk away!
What you should do is look for a running car with current tags (no back taxes) and clear title. Start from there. Don’t even consider buying a car with major problems like this if you don’t even know what a head is. You won’t want to fix it yourself and you won’t like having to pay extra and wait longer to get a running car. It is inconvenient.
I don’t agree that you should always take a used car to a mechanic, especially a special dealer mechanic, before buying. It depends whether or not you know what you are looking at. I bought my 1970 VW for less than what you’re about to pay around 2008 and it still runs fine. Just did a self inspection before buying. When you’re only paying a grand, you don’t stand to lose much anyway if it turns out to be a lemon.
Finally, when you call this car “perfect” it sounds like you’re referring to the aesthetic. That’s the last thing that matters when you’re trying to get from A to B. Be practical.