No all fields DO NOT fill HPA. The compressors required to fill them are incredibly expensive and the alternative is a bulky and complicated cascade system. Many fields and small fields in particular are still sticking with simple and affordable CO2. The reason steel tanks are cheaper is that put simply they just aren't as good or useful. A steel HPA tank holds less air and weighs much more than a carbon fiber tank.look what this guy said about hpa:
rest assured, all paintball fields fill hpa tanks.
from personal experience i recommend zephyrpaintball.com, paintballgateway.com, and actionvillage.com if you are looking online. local paintball shops may be willing to cut you better deals than what you can find online though and it's always nice to support your local shops =]
some reliable brands are dxs, guerrilla air, and crossfire. these all range around the $150 area if you want a carbon fiber wrapped tank. if you want to settle with a steel tank the price drops considerably to around $60.
why does the price drop?