Aulas had earlier denied reports the star forward was in London to undergo a medical, indicating the Premier League club were yet to meet Lyon's asking price. Goal reported Sunday that Lacazette was expected to sign a five-year contract with the Gunners.
The club chief later confirmed a deal for Lacazette was almost complete, with Arsenal to pay up to €50m for the France international.
"The figure reported by the English media of around €67m [including €12m in add-ons] is impossible and not realistic," Aulas told Le Progres.
"Arsenal's first offer was around €45m, the transfer will be concluded in the range of €45m to €50m."
The deal would signal a club record for Arsenal, who paid Real Madrid €44m to sign Mesut Ozil in 2013.
Aulas talked up the fee, saying: "Being close to €50m is something unique and will probably be a record for Arsenal and Lyon as well.
"Knowing that, traditionally, a club like Arsenal — and this is the case for Bayern Munich also — don't invest so much on a player."
He has 11 France caps and has made more than 250 appearances in all competitions for Lyon.