Yeah, I've seen some absurd ones (cheap) on other airlines (my friend got $100 for upgrade to first from MCO/LAX; ETA: on Alaska) and I've seen some absurdly expensive ones on int'l itineraries.
I've done $600 cash from BOM/LHR to 1st on BA, which got me in the CCR in LHR for 4 hours on top of the plane upgrade. And I've often seen... $500 (maybe $700? Now I'm self-conscious) from NRT/LAX on AA advertised at the counter.
I think, domestically, the standard AA exchange rate is $50/500 miles or so (roughly)?