When was the Benjamin Model 340 T 36211 made and how much is it worth?

To answer the first part of your question: It was made in 1969.

As for the second part of your question (How much is it worth)... If I asked you How much is my 57 Chevy worth, without giving you any description of it's current condition, I don't think you would be able to give me an estimate of any value. It's the same with airguns. It could be a GEM or a DOG. You need to give more information, Give it some sort of rating like It's in, poor, fair, good, very good or Excellent condition. Then I have some way of giving you an estimate of value.

Also. The next time put your air gun question in the "Air Gun and Air Rifle" category and it won't take me 10 days to find the question.