Adam Lambert -- Worth WAY More than $80K in Russia ... According to Lawsuit

Adam Lambert would NEVER perform in Russia for less than $500,000 -- this according to a new lawsuit, in which a promotional company claims it was conned into thinking it could book him for a fraction of that price.

UK-based Madison Universal filed the lawsuit against a talent agency in Santa Monica named Family Productions -- claiming FP promised to broker a deal in which Adam would perform two concerts for $80,000 ... one in Ukraine and one in Russia.

Madison claims it paid FP a 10% deposit of $8,000 -- but FP didn't do squat to line-up the concerts ... so Madison tried to get its money back ... to no avail.

According to the complaint, Madison grew suspicious -- so it contacted Adam's agent Randy Salcedo at CAA -- who informed Madison that an $80,000 fee wouldn't cover a Lambert concert in Russia ... let alone an additional one in Ukraine.

According to the suit, the cost for flying Lambert out to Eastern Europe to perform is more accurately $500,000 ... or more.