The Seattle Seahawks' defensive back core held its annual rookie dinner Monday night ... and a pair of first-year NFLers were hung with a $17,500 check!!!

The booze-and-steak-filled night all went down at Daniel's Broiler in Bellevue, Wash. ... and according to some of the vets, it was the most expensive rookie dinner in a while.

The receipt is absolutely nuts ... the guys bought a TON of expensive food and alcohol, piling up $11,000 worth of Louis XIII alone.

There was also Wagyu steaks, lobsters, calamari and all the fixin's ... and in total, the bill came out to $17,579.10!!!

As for the guys who whipped out the credit cards for the check ... Ugo Amadi and Marquise Blair were saddled with that task -- but neither seemed to be too pissed (at least judging by the videos we've seen).

Of course, perhaps they should've been ... neither is signed to that big of a contract -- Amadi is on a 4-year, $3,165,196 deal, while Blair inked a 4-year, $6,236,648 one.

But, hey, at least the vets seemed to appreciate the gesture ... with second-year corner Tre Flowers saying, "I been waiting on this day for a year lol."

The rookie dinner is nothing new in the NFL -- it's been going on for decades ... with Hall of Famer LaDainian Tomlinson previously telling TMZ Sports he had to pony up some major dough when he was a rookie in 2001.

"The late Junior Seau and the veterans hazed me by taking me to dinner and spending $18,000 of my money!" LT said.