From Chengdu to Guilin, both trains and flights are available daily. It takes about 25hrs by train while just around 1 hr and 25mins by air. And it cost about CNY250 for one soft sleeper. Besides, u can also get a cheaper air ticket as the airfare of the domestic airlines always has discounts. You could visit Chengdu flights(https://www.travelchinaguide.com/china-flights/chengdu.htm) to check the exact airfare with your travel date.