Every offer I've heard this year was $400 (and I took one), though the kiosks have asked me several times at lower amounts (ranging from $75 to $250). GAs have seemed to have a hard time finding takers even at $400 IME--even when the next flight was less than 2 hours later.

Depends on the route, time & day of week, and pax demographics IMHO whether or not you'll get takers at the lower levels.