Lil Uzi Vert didn't skimp on his girlfriend's birthday -- the guy rented out a whole theme park for her ... which cost him a pretty penny and then some.
The rapper took over Nickelodeon Studios Park at the American Dream Mall in New Jersey -- with about 20 of his buddies tagging along for the festivities Friday ... all in honor of JT's 29th birthday. JT is one half of the City Girls, and has been dating Uzi for a while now.
Anyway, sources familiar with the excursion tell us it was about $50k or so to get the whole place to themselves. Even though it's inside a shopping center, the park is decked out with dozens of rides, including a roller coaster and a Drop Zone type of attraction.
Speaking of those ... Uzi and JT were front and center for a lot of those rides, posing for pics and looking like they were having a blast.
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There were more than just thrills to be had, BTW ... Uzi gifted JT a new car as well -- a McLaren, no less -- among other things, which she seemed to appreciate.
One last thing ... Uzi didn't ruin anyone's else good time by booking NS for him and his crew/boo -- we're told they did all this after hours, so folks were able to enjoy it during the day.