Currently there is no direct bus from Shijiazhuang to Beijing Airport unless taking a cab, which costs about CNY1,000.

Well, you could take a train from Shijiazhuang to Beijing West Railway Station firstly. The express train only takes about 2 hours en route. And then, at Beijing West Railway Station, you could take shuttle bus Line 7 or a taxi to the airport directly.
The train schedule could be searched on this page: https://www.travelchinaguide.com/china-trains/beijing-schedule.htm