Today I made the run to our local home improvement center (called Menard’s, similar to a Lowes or Home Depot) and purchased the materials for the terrain mat.
This mat is intended mostly to represent North West Europe. I will be using it for SAGA and for various World War II games, and in various scales as well. To that end, I wanted a base color for the mat that was fairly typical of that region’s soil. I chose to use Vallejo’s Flat Earth as the base color for a couple of reasons. First, it is fairly close to a typical soil color for the places I am representing, especially after shading and dry brushing to break up the tones. Second, it is the base color I have used on my miniatures for years, and I love to be able to mask the bases of the figures as much as possible.
Obviously the cost of using Vallejo paint to cover a play mat 6 x 9 feet in dimension would be ridiculously expensive, so I used the paint departments color matching and had them make a quart of it (approximately a liter). I am hoping this will be enough, but if it is not, it should be easy enough to get another.
The finished mat will be 5 x 8 feet, so I selected a heavy duty canvas drop cloth to use as the base. There were a wide variety of sizes available, and one could create an absolutely huge terrain mat if they desired. The best size for me was the 6 x 9, allowing me a foot to cut off the outside when I am done.
Then came the caulking. It took some digging to find the latex acrylic caulking that did not have silicone added to it. I was not sure if the addition of silicone would affect the paint or not. I suspect it would not matter, but finding latex acrylic caulk without it saved me the worry. I probably bought more than needed, but have plans to make a desert mat if this works out well, so I can save it for that project.

The list of materials with cost breaks down like this:
1 6 x 9 Canvas Painters Drop Cloth $9.50
1 Quart of Latex Enamel Interior House Paint matched to Vallejo Flat Earth $10.50
6 Tubes of Latex Acrylic Caulk $1.74 each, so $10.44
Materials not pictured, but either free for me, or things I already have on hand:
A copious amount of sand, free from the driveway.
A wide variety of flocking of differing shades and textures.
A putty knife.
A large wooden table which I can leave the cloth attached to while I work.
My total cost so far is about $30, and I do not foresee much more expense. If it works out well, it should be a fairly flexible and cost effective terrain mat, and with any luck, it will look good too.