Tianjin is less than half an hour by high speed train from Beijing's South Train Station, and one and a half hours by regular train or car.
First class tickets on the high speed trains are about $13.00 USD and for coach about $9.00 each way. All cars are super modern, clean and spacious, as are the train stations. You'll be traveling at 350 km per hour. Tianjin is a very friendly city, and much less hectic and crowded than Beijing.