Lamar Odom -- Drugs Are Expensive ... But Porn Isn't

In what could be a significant cost-cutting move, Lamar Odom has added to his obsessions -- but unlike his serious drug problem ... his newly acquired porn pal is free.

Lamar has set his sights on Tube8 -- according to his Twitter page -- a site that touts, "Everything always tastes better when it's free, including porn."

It's unclear when Lamar and Tube8 linked up, but Lamar is very fussy about what he follows. And only follows 50 celebs ... including Justin Bieber, Floyd Mayweather and the Kardashian/Jenner clan.

So for the time being, and clearly not of his own choice, Lamar has replaced Khloe with about a thousand other cool chicks.