Most soccer matches, especially rec games, are usually at night and on weekends. And if you're working with a local association, travel really isn't an issue. Even if you're always an assistant on a U12 game as a grade 9 referee, you should be able to recoup your certification costs after just a few games.
Now, if you want to work out-of-town tournaments, yeah, there's travel involved. But most tournaments I've worked pay mileage and a per diem. Some pay for your motel. But you often only get into those tournaments if you're a grade 7 (or sometimes a grade 8) referee - and you only can move up to those grades if you've reffed so many games, gotten positive assesments and passed a fitness test.