A good compromise is to just run the actual machine in your house and rent a VPS for the sole purpose of installing a VPN server to provide your machine at home with access to a static IP address that doesn't have outgoing SMTP blocked. That way all the VPS is doing is forwarding data to and from your machine at home and it doesn't have access to anything your ISP wouldn't, and TLS/PGP/etc. goes a long way to help with that as well.

That should keep anyone from reading your email (assuming you and other senders are using TLS), but the next problem is that an ISP-level observer can always tell who you're corresponding with unless you use something like mix nets or Tor. And allowing that requires some cryptographic authentication method to distinguish legitimate anonymized senders from spammers without leaking the sender's identity to an intermediary. Having the sender sign the message and then encrypt the message, the signature and anything else that identifies the sender with the recipient's public key ought to do it but I'm not sure if there is any existing software that will actually do that. It might be possible using a combination of PGP to authenticate the sender and SMTP TLS over Tor to actually transmit the message, but the missing piece is for the sender authentication to be integrated with the spam filter.