Any travel agency will have trips to Huanglong and Jiuzhaigou. A three day trip that includes everything (air tickets, hotel, all meals except for one day inside the park, entrance fees to both parks) runs 800 to 2500 yuan depending on the season; they've been around 1000 lately but will be getting more expensive soon with the warmer weather. The cheapest tours do include shopping stops, which are a little annoying.

I'm a Sichuan local guide,I'd like to help you.
Basically, there are buses from Chengdu Xingnanmen Bus Station to go to many of the scenic spots in Sichuan. The bus ride to Huanglong is 8hours quite slow due to the poor road condition,but the scenery is pretty on the way. You can also take a flight to go there, If you just want to visit the Natioal Park or some touristy places, you can reach by yourself, and better to hire a local guide if you wanna visit some area beyond the tourist spots.
www.sichuan-private-guide.com

Check out the Chengdu tours and activities from Ctrip, there are some good low season prices at the moment for trips to Jiuzhaigou:

http://activities.english.ctrip.com/city/28-chengdu-tours/