We would like to go for the week-end to Pingyao. How to go there from shanghai?

Oh, there is also no direct train or long-distance bus that runs between these two places.
You can take a train to get to Taiyuan Railway Station first. The duration is about 20 hours.
The ticket fare of soft sleeper is CNY509.5 and hard sleeper is CNY331.5.
Then transfer a train to the destination directly. It takes nearly 2 hours. Soft sleeper costs around CNY 102.5 and hard sleeper costs around CNY70.5.

Tom's way is doable, but it takes quite long. Personally, direct flight to Taiyuan and a transfer to PY is the best way. It doesn't cost much as you said. Sometimes, many airlines offer great discounts. You'd better compare several airlines.

To save time and money (by air), here is another way for you: take a high speed train to Zhengzhou and then transfer to another one to Taiyuan. Afterwards, take a high speed train to reach in 30-40min or a long-distance bus to arrive in 2 hours.

Choose a way among these solutions.