Provided that it doesn't need a new turbo or transmission, I have a feeling that most of that stuff isn't too huge. Fuel filters, valve adjustments, window switch, all relatively minor items. If the battery problem isn't with the battery itself, alternator attention might be needed, or, it could just be a loose belt not recharging the battery properly. Could just be a bad battery. The heat problem is simply a mono valve fix which'll cost you about $22. Good luck, I think that model's a nice car.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside