2002 Dodge Caravan Check Engine Light

The check engine light came on a couple of months ago. I took it to a shop that retreived codes P0740 (Torque converter clutch circuit malfunction), P0700 (transmission control system malfunction), and P0306 (cylinder 6 misfire). The car seems to run fine, and the transmission guy drove it around and said that apart from the light nothing seems to be wrong. Unfortunately, he said that taking out the transmission to diagnose the problem properly would cost at least $1,100. Which is a lot for a car with a blue book value of $2,800, especially since that is for the diagnosis and does not include any actual repairs.

The check engine light is an automatic "fail" for a smog check, which means I will not be able to sell the car or renew the car's registration when it expires in a couple of months. What do you suggest I do? It seems crazy to have to junk a car because of a light when the car runs fine.