Kylie Jenner -- 18th Birthday Bash Made Everyone Involved a Fortune!

Kylie Jenner's 18th birthday party in Montreal was big business for everyone involved ... not only did Kylie make big money, but the club AND the promoters scored six-figure paychecks.

According to our sources, Beachclub raked in $150,000 for KJ's big day, while the promoters took home around $100,000 (they took in $300k at the door, but paid Kylie $200k to show up).

Beachclub's owner, Olivier Primeau, wouldn't comment on how much was made, but tells TMZ he spent an additional $30,000 just to make sure the night went flawlessly. Here's where some of that extra money went:

-- $1,500 to build a deck so she wouldn't have to walk in the sand in her heels.

-- $4,000 for 2 specially built private bathrooms near the stage, so Kylie wouldn't have to go thumping through the crowd to use the restroom.

-- $10,000 for security, which included 100 security guards.

Think of it this way ... Obama's inauguration probably costs more.