Actually, that $700 outlay for a decent stereo would be much more today.
$700 in 1966 is equivalent in purchasing power to about $6,570.65 today, an increase of $5,870.65 over 57 years. The dollar had an average inflation rate of 4.01% per year between 1966 and today, producing a cumulative price increase of 838.66%.
All said, that amount would get you a mighty fine system today.
All the best,
Nonoise