Jo, this is just an idea, but it's what we're doing so our girls can run outside. This fencing comes in a big roll of 100 feet for $60 a roll. The fence stakes are about $5 each. The holes are maybe 2" x 4", plenty good enough for a small dog. It comes in different sizes too for not much more money. It's called Red Brand Fencing I think...
I figure we can fence my back yard for under $100.