Is there a difference in "Fill Sand" vs. "Paver Sand"? When quoting prices for laying a patio, I'm finding that Paver sand is about 10 times the price. Will Fill sand be sufficient if packed well and laid thick enough?

You want to use a sharp sand under the pavers so it can be screed and tamped down. Finer sand will wash away. You can buy it by the scoop at a Builder's Supply pretty inexpensively. I personally have used Deconstructed Granite, (DG), and it is around $20 a scoop.

Over the top of the pavers you would use Polymeric Sand which is a finer sand with a Polymer Additive, after pouring it over the pavers and sweeping it into all the joints and crevices, follow up with water and the Polymer will help seal the joints and cause them to hold together.

What type of patio are you having installed? Stone, pavers? What is your climate - does it freeze in the winter? And how large of gaps do you anticipate between the stones? Washed sand is a more expensive material, and many paver companies use this as a base. Depending on your climate and circumstances, a Bedding sand - which has some dirt in it - may actually work better and be far less expensive.