Near the end of its service, the regular fare was something like $12,500 roundtrip. If one planned in advance, there were various types of sales.

In terms of miles, for BAEC North America, before changes that took effect July 1, 2003 (just a few months before the end of service), I think that North America to Europe was

40K Y low season
60K Y high season
80K J
100K F
125K R
One could not necessary mix-and-match all combinations of class of service, but there were certains where you could:
One-way Y, one-way R was 90 or 95K
One-way J, one-way R was 110K.
(One-way F, one-way R was, I think, 125K. Not sure about one-way WT one-way R).

Effective July 1, 2003, BA adopted its current structure.
North America - certain parts of Europe was 50K in Y, year around
J was 2x, F 3x, and R 4x.

Before 6/1/03 one could fly from the west coast of the US all the way to the 'Stan countries in Central Asia, F across the US on AA, R across the pond, and J across Europe, for 125K roundtrip (they were part of Europe).
That same trip probably become 240K or 320K.

US to Oz in R over the pond and F elsewhere was, I think, something like 175K, a true bargain. After 7/1/03, I think that probably become 560K.