We know they had some help.

Luke 8:1–3

1 Soon afterward he went on through cities and villages, proclaiming and bringing the good news of the kingdom of God. And the twelve were with him, 2 and also some women who had been healed of evil spirits and infirmities: Mary, called Magdalene, from whom seven demons had gone out, 3 and Joanna, the wife of Chuza, Herod's household manager, and Susanna, and many others, who provided for them out of their means.

So it sounds like these were some wealthy people who provided for Jesus and his disciples as they traveled. It was also common for people to host a visiting rabbi and provide food for them. Jesus and his disciples were often invited to eat at people’s homes. In fact, when Jesus sent out his disciples to do their own missionary work (Matthew 10, Luke 9) he told them to rely solely on others’ generosity for their provision.

There wasn't always a steady supply of food and shelter. At one point, at least, the disciples picked some grain from people’s grainfields (as allowed by Mosaic law) to eat. Jesus also talked about having “no place to lay his head” (Luke 9:58).

So that probably sums it up. It wasn't as though they lived in abject poverty, but it was no steady income either.