I'm not sure what the going rates for day hire of a chauffeured car are in the Yarra Valley, but I don't imagine that's going to leave you a lot of change from $1000 for two days! I'd advise you to look into other options: bicycle (the Warburton Rail Trail is great fun), self-driving rental with a designated driver, or any of the dozens of small winery tour companies (10 people or less, $100/person/day and up).

If you're planning on spending two full days in the Valley, then staying there is the obvious option. It's a bit of a hike from Melbourne and the journey to get there is remarkably un-scenic.

AFAIK, you're not going to find anything remotely like a "dive bar" in Yarra Valley, most wineries target the wedding market and are themed to match. But "rustic" you can certainly do, esp. if you get in touch with the many "by appointment only" places.

Also, if you like reds & pinot, have you considered the Mornington Peninsula? It's famous for pinot noir and a destination in itself, more popular with locals than the tour group set. Easy to get to from Melbourne as well now that the Peninsula Link motorway is open.