Sunbabies are cheap. They run small though so I would not expect then to fit until potty training.
I like sized prefolds and one size covers for the cheapest working cloth option. But I don't recommend the cheapest covers out there. Instead I recommend getting good covers from The Fancy Pansy on HC as they will last longer and fit better.
I recommend getting prefolds from GMD. They have seconds sales every so often and they post them on their FB page. That would be the cheapest way that works in my opinion.