Economical VPN to Peer-to-Peer Intranet

We have a peer-to-peer intranet, utilizing a server running NT4.0 workstation for common files and minimal security. The lan has a 300K connection to the internet. Each lan workstation runs IBM Client Access to communicate with our AS400, which wealso want to be able to access remotely via the VPN/internet. We cannot afford an upgrade to NT Server right now. Is there an inexpensive way to give our remote users VPN-style access to our intranet via their personal ISPs?