Since litigation is costly, the acceptable range for a settlement is centered around the expected outcome of a trial, plus or minus each party's cost of litigation (including opportunity cost).
In this case, "the claim is barred by the statute of limitations" implies that the expected outcome of litigation would be approximately $0. The net range for a settlement is then the 'nuisance value' of a lawsuit including any PR damage for airing the case publicly; that would be orders of magnitude below the $1bn claim.