Jiuzhaigou

You can take direct buses at Songzhou Bus Station on the north of Songpan Ancient Town to Jiuzhaigou and Huanglong. You can share a car with other tourists in Songpan and need to negotiate the price with the driver. It may take CNY 300.

300 per person or per car?

Per car.

I have checked the bus from Songpan Songzhou to HuangLong only departs at 6am, 7am & 14pm.
If I take a coach from Jiuzhaigou at 07:50, arrive to Songzhou around 10:00, then only take a bus at 14pm to Huanglong, is that correct?

I saw in others' shares saying that Songzhou Bus Station - Huanglong bus departs at 10:30 and 12:50. And I see no direct bus from Jiuzhaigou to Songzhou at present, maybe it's because the Huanglong Jiuzhai Railway Station is open.
And there are direct buses from Jiuzhaigou to Huanglong departing at 08:30, 08:50 and 09:20.