The figure compares with £515m at the same stage in 2015 and an £870m outlay in the whole of the 2015 summer window.
Leroy Sane's £37m move to Manchester City, confirmed on 2 August, is not included in the figures.
Deloitte says gross outlay could rise above £1bn for the first time before the window closes on 31 August.
Manchester United could bump up the spending significantly if their reported £100m move for Juventus midfielder Paul Pogba goes through.
The Premier League starts a new £5.1bn three-year television deal this season.
"The prospect of increased revenue from the new broadcast deals next season has encouraged Premier League clubs to invest in this window in order to be as competitive as possible," said Alex Thorpe, senior manager in the sports business group at Deloitte.
"With a month of the window still to go, some significant deals in the pipeline and a number of clubs yet to enter the market, we may see another summer of record Premier League spending, possibly breaking the £1bn barrier for the first time."
Sky are paying £4.2bn and BT £960m for the rights to show live top-flight matches over the next three seasons and, as a result of the deal, each club can expect to receive between £30m and £50m from the Premier League for 2016-17.
The combined total spent by Premier League clubs over the summer and winter transfer windows last season was £1.045bn - up from £965m for 2014-15.