The 24-year-old scored his sixth goal in as many games on Saturday as the Hammers beat Burnley 3-1 at Turf Moor.
Having joined the club for £3.5m in the summer from French outfit Metz, Allardyce believes that Sakho is having a big impact at the club both on and off the pitch.
"He is a bargain. This lad has been very exciting and he's excited the rest of the players," he told talkSPORT.
"I think all our players that were here last season, having had some of the depressing times that they didn't expect, have all been lifted by the new players and their performances have increased as well as the news lads hitting the ground running.
"We just hope it continues. It's too early to say what we're going to be or what we're going to do but things are looking very good. If we get into December and we're still getting results and maintaining a top-half position, then we can start thinking about maybe maintaining that for the rest of the season."
West Ham are currently fourth in the Premier League table following today's victory.