2000 Chevy Venture Do I fix this vehicle?

I'm at a cross roads on whether to fix this 2000' vehicle. It has 120,000 miles & it needs a transmission plus a new gasket at the intake manifold. I'm quoted on the repair for $2800. The Kelly Blue book for this vehicle in "good" condition= - trade in value is right around that value. Is there a formula when it is wise to repair/junk a vehicle.