Ariel Winter -- Buys New Mercedes ... PAYS IN FULL

Unlike most 16-year-olds -- who scrape together money from their part time job to go halfsies with their parents on a used Ford Taurus -- "Modern Family" star Ariel Winter just picked up a brand new Mercedes ... and paid for it in full.

Winter hit up her local Mercedes dealer recently and scored a fully loaded C350, blacked out with the AMG package. We're told Ariel and her sister went in with the idea of getting something nice, but also responsible and safe.

Our sources tells us Winter's dad -- who only recently began siding with Ariel and her sister in their battle against Ariel's mom -- was there to help her sign the papers. Once the deal was closed, Ariel wired the full payment ... just north of $50,000. APR financing is for suckers!

And get this ... the guy in the photo, who sold Ariel the car, is former soap star/current car salesman Matt Borlenghi. The funny part is ... Ariel's mom sued him for defamation in 2012.

Probably not a coincidence.