Hey Optronic and welcome!
You cheapest option would be a Compact Flash WiFi card. It wouldn't give you internet access everywhere you are, but in a good many areas (depending on where you are) like Starbucks.
Your other, more expensive, option is to get a CF bluetooth card and a cell phone with bluetooth. Sign up for your carrier's unlimited data access, pair your phone with your Jornada and you'll have internet access anywhere you've got a cell signal. If possible, get a phone that can connect at higher speeds than GPRS (like EDGE UMTS etc.) - that will provide a more enjoyable mobile online experience.
Hope that helps!
amion