Taicang City is under the control of Suzhou City where there is no airport. So, if you would like to fly there, firstly you have to arrive at Shanghai Pudong Airport from Beijing. The airfare could be search at https://www.travelchinaguide.com/china-flights/

From Shanghai, you could take a coach to Taicang in 1.5 hours with a ticket of 21rmb. The coach station is located at the north square of Shanghai Railway Station. From the airport, shuttle Line 5 will drive you to the south square of the railway station in no more than 1 hour. And the fare is 22rmb.

Alternatively, it is convenient to take the express bullet train from Beijing Railway Station to Shanghai Railway Station directly within 10 hours. Then, transfer to the bus to Taicang easily.
The train information is listed at:
https://www.travelchinaguide.com/china-trains/