Chumlee to Girlfriend -- HAPPY BIRTHDAY! Here's Some New Boobs

"Pawn Stars" pays BANK ... just ask Chumlee ... who dropped thousands of dollars on an expensive new pair of boobs for his girlfriend, TMZ has learned.

Sources close to Chum tell us, the perky new breasts were a recent birthday gift for his gf Tanya -- but that wasn't all he got her.

We're told Chumlee also rented out a penthouse suite for him and his lady at the D Casino hotel last weekend, paid for several lavish dinners at the hotel's Andiamo steakhouse -- including one attended by Tanya's 11 girlfriends -- and even arranged fancy limo rides through Vegas for her and her family.

And get this ... after dinner Saturday night, Chum hit up the high-limit blackjack table ... where the minimum was $500 per hand.

Chumlee tells us, "I wanted it to be the best birthday ever for her and was happy to be a part of a great party, celebration, and special gifts."

Hehe ... special gifts.