Cheapest way to improve a path?

[WellTidy]

We have a path alongside our border, running the length of the garden. So, as you look at the left side of our garden from the house, it is border, then path, then lawn. The path is uneven concrete, splitting in parts, and is wider in some parts than in others, and basically looks tatty and uncared for.

I am looking for the cheapest way to make it look better! I would like it to have a straight edge onto the lawn and for it to look even. But I don't know how to accomplish that. The garden is about 80 feet long, flat.

We had one a bit llike that. We used old paving slabs (salvaged from a patio re-paving job), bedded on sand on top of an old rough, irregular concrete path. There's a gap to one side between the slabs and the fence, which is filled with gravel, and the lawn butts up directly to the other edge. It's been there for nearly ten years now, and seems to work OK.