Yes, on PeopleExpress you could pay on board. The f/a's would go down the asile with a cart with a credit card processor and a cash box. Of course you couldn't do that today! On domestic flights, PEX usually between $ 59 to 129 o/w + taxes and $3 for each check in bag. For their Service to London and Brussels, was sometimes 99 + tax o/w but usually $149 o/w +taxes/fees.
Shortly after deregulation, coast to coast or northeast/Florida fares were often $99 + taxes each way or less on LLC's or if bought a bit ahead, like 14 days on majors. Many majors serving NYC/LHR
or Paris, used to offer standby fares in the 1980's-early 90's of $149-249 o/w + taxes.
Often these cheaper fares varied according to time of year, day of week.
I believe the original Eastern Shuttles between LGA
were originally priced at $19-29. Now that is about $220 o/w walk up price or the same for an advance purchase r/t.