Late 1980's: MCI-MDW wasn't hard to get for $19 or $29 each way. I remember paying cash at the airport to fly Midway Airlines once.

Early 1990's: Bought my first TATL as an "open-ended" fare on DL. Outbound was on a fixed date, but the return could be on any date within one year with a 72-hour advance booking requirement. MCI-ATL-LGW-ATL-MCI was $775 R/T, outbound in September, inbound in June.

Same period, multiple Birmingham and London to/from U.S. roundtrips, I got better at booking these and booked some through a student travel agent. Got a couple for around 300 pounds R/T, which ended up being a decent fare as the pound had retreated from $2 to the $1.50-1.60 range.

Late 1990's: probably my heyday for dirt cheap airfares. Living in Chicago, so had plenty of competition and promotions to pick from. Many ORD-Europe R/T's over a five year period in the $400-500 R/T range. Even a couple sub-$400 on AA. Always off-peak of course - February and March being the optimal months to go. With occasional route bonuses and Plat status on AA, these trips would sometimes crank out 20k+ RDM's. Of course everything was upgradable with no copays.

Early 2000's: flew a bit less international but still picked up a lot of cheap domestic fares. West Coast for under $200 R/T, East Coast or Florida often for $59-69 each way. I was doing UA during that period ex-MCI, but Southwest was still the initiator of fare sales out of MCI. So I'd watch their sales and then watch to see if UA matched, which they often did.