Then obtain a server (or a friend with a server) outside of your school's network, and encrypt your communication through it. A commercial server (or virtual machine) may be cheaper then a private ISP connection.
But you still must trust the remote server, and its network(s).
There's lots of choices of traffic encryption technologies. What to choose will depend on your network applications and your network topology. But, without a system external to your untrusted-network, its academic.
Regarding topology, your network traffic rules may disallow any or all of these:
- An IPSec-based VPN can efficiently encrypt all traffic.
- An OpenVPN-based VPN can encrypt all traffic via UDP (or TCP) between end points
- An SSH-based VPN can tunnel all traffic via TCP between end points
- An SSH-based SOCKS proxy can tunnel all HTTP/HTTPS traffic between end points
These all have the same effect, with varying amounts of efficiency, ease of use, and capability. Traffic from your system(s) is encrypted and is sent to a remote end-point, which decrypts it and relays it to the final destination. Traffic to your system(s) is encrypted at the remote end-point, and gets sent to you for decryption and final disposition.