Casper Smart -- Hey J Lo, This Trip's On Me!! ... Sorta (PHOTO)

Casper Smart could be treating his gf Jennifer Lopez to a romantic trip for two in Saint Martin ... but he won't pay a dime for it.

Casper was at the GBK Oscar's gifting suite at the London Hotel in LA Friday to rack up nearly $20k in goods. The best item up for grabs? A free trip for two to Saint Martin, the perfect getaway for J Lo during her Vegas show and American Idol judging.

It's unclear if Casper cashed in on the vacay for himself or if it'll go to a friend -- but one thing's for sure -- the best kinda vacations are free.