Jermaine Dupri -- Sued Over $80,000 in Unpaid Lamborghini Bills

Not only was Jermaine Dupri's mega-expensive Lamborghini repossessed recently -- now, the people who fronted him the cash to pay for it are out for blood ... claiming the producer still owes them $80,000 for the car.

Premier Financial Services filed new legal docs in Georgia Superior Court, claiming Jermaine financed the white 2005 Lamborghini Murcielago in 2006 -- worth $330,000 -- and agreed to make 58 monthly payments of $4,323.

According to the docs, Jermaine dropped $70,000 up front for the car and successfully made the majority of payments -- but for some reason ... he dropped the ball in 2009, and failed to pay the remaining handful.

As a result, PFS repossessed the car and sold it off for $115,000 -- and now they're out for the difference ... insisting they hemorrhaged $79,095 in the deal-gone-wrong, and they're suing Jermaine for their losses.