Control packets with pfctl
PF (Packet Filter which command line interface of is pfctl) can't do this, because it's not application but port/interface based. You may block port 80/443 for a web browser (like Safari) but this will also block Mail fetching an web-based embedded picture in an email.

Your best bet is to use a host-based application firewall like Little Snitch. The app allows a fine-grained control of outgoing traffic. You may even allow a browser to connect to text based (low traffic) websites while blocking all other sites.

You can even set up several profiles for low- or high-bandwidth locations.