This page describes four Gibson flat top acoustics, the J40, J45, J50 and J55 - though the J50 is not pictured.
UK prices (1981) were as follow: J40, £789; J45, J50 and J55, £829.
$6750
$6300
$6000
$4700
$4599
$3500
$3500
$3000
$2700
$2550
$2190
$1520
$1300
$795
$795
$795
$795
$710
$670
$495