The other comments here are good. Also remember that there are EDI services that start around $100 a month that will make the process easy when the time comes.
It's rare that a new vendor gets picked up by large retailer that requires EDI right out of the gates, and if you do, it isn't necessarily difficult to become EDI compliant in a hurry. The vast majority of specialty retailers don't require EDI so I wouldn't worry about it in the beginning. EDI is something you can grow into... There are far more pressing matters to concern yourself with before you get to that point. Spending a few dollars on consulting can save you thousands when you are just starting out... Good Luck to you!
Francis, it depends on the retailer. Some large regional chains allow you to utilize Web based PO transmission. The routing guide of each retailer will share the specific information. I recommend an experienced Rep to support your efforts in vendor negotiations.