I'm not in the habit of trying to promote peoples ebay items but I must pass comment on this because it doesn't come up too often.
The Speedtrack Grand Prix 1000 was the largest of all the Powertrack sets. This set stands out because it is a 1977 set and seems in pretty fair condition for its age. 1978 versions had four cars but this set has the ever present Porsche 911 & Corvette duo.
The cars are in beautiful condition and are the very rare white wheeled examples. The Corvette even has the stripes on the doors.
There is a ton of track here and okay, while it's not brimming with features it will certainly be a good launchpad for someone to start Powertrack with. You may have to junk the electrics but I suspect without too much fettling this set is a bargain for around £10 + shipping.