The ferry Herjólfur is departing from Landeyjahöfn harbour. It is a 2 hours drive from Reykjavik along the Ring Road in direction south to Landeyjarhöfn and the sailing time of the ferry is approximately 35 minutes.
You can take your car with you to Vestmannaeyjar which costs depending on the size 3,300 ISK til 4,400 ISK. Prizes for trailers and other vehicles can be seen at the homepage of Herjólfur.
Insider tip: When driving to Landeyjahöfn I recommend to stop at Seljalandsfoss and take a walk to Gljúfrabúi as it is directly on the way.