Lamar Odom -- $800 Per Day Summer Drug Habit

Lamar Odom fell deep into the world of hardcore drugs during a wild summer in Hollywood ... where he spent as much as $1,000 in a single day to fuel his growing addiction to crack -- according to sources familiar with the situation.

TMZ broke the story Lamar was hooked on crack -- but now we've learned just how bad it got in the last few months.

We're told Lamar's habit picked up speed when he moved out of his home with Khloe Kardashian, and into Hollywood's Roosevelt Hotel with a friend in late May ... after the NBA season ended.

We're told the hotel room was used like a flop house ... where Lamar was surrounded by his pal and 7 or 8 other drug abusers -- strangers -- who came in and out of the room throughout the day and night ... for several months straight.

According to sources, Odom was dropping -- on average -- $800 per day, but sometimes more, for multiple drugs, including crack.

By the way, if $800 worth of crack sounds like a huge amount of drugs for one person ... it is. But we're told Lamar sometimes shared his huge score. Plus, drug dealers often charge rich customers premium prices.

As we first told you, Khloe kept Lamar's drug addiction secret for at least 2 years -- but after this summer she decided enough was enough ... telling him if he didn't get treatment, she would pull the plug on their marriage.