The Saints signed Austin for a fee of just £4 million (Daily Mail), and Bilic admits that he was surprised to see the 26-year-old move so cheaply.
The Croatian boss has backed Austin to prove a bargain at St. Mary’s, but he says West Ham never made a move for him.
“He is a great player,” he said. “He is not one of those who has just done it in the Championship and there is a bit of a question-mark because Charlie scored many goals in the Premier League in the season that QPR got relegated.
"To get him that sort of money – and then have him score the winner in his first game at Old Trafford – he should be a great buy.
“I was a little bit surprised he went for that money in England. He is definitely a player with the quality to play for the West Ham and most teams in the Premier League, but we had different targets. We have enough strikers and were hoping for a different type of player.”
The Hammers were persistently linked with Austin throughout January, but they ended up signing Emmanuel Emenike on loan to bolster their striking ranks instead.
Austin will now be looking to show the Hammers exactly what they are missing at the weekend.
Southampton are due to host Bilic’s men at the weekend, in a match which could be defining for both club’s seasons.
A win for West Ham could see them build up an eight-point gap over the teams below them, while a win for Southampton would put them in the thick of the hunt for a European spot.