[RPG] How to make the own battle mats

Premise: I live far from the US, and for me, paying U$S20+shipping for Chessex Battle Mats is out of the question (I just spent U$S 114 for a full lineup of DnD Essentials, and this extra expense would be a great way of getting killed by my wife).

I thought that I could make my own battlemats, or having them made locally, buying the material in a hardware store / paper store and either having it etched / permanently colored with grid lines or doing it myself (a nice slow work for a rainy afternoon).

What I want is something

• durable and persistent: paper sheets work fine, yes, but they're one-use only, and I have to redraw the grid for each new sheet.
• portable: I think that this solution is a bit less encumbering than a dry-erase board, especially at the sizes I'm thinking: I want something I can carry with a backpack, if possible. With the proper materials, I can just roll the mats into a tube, or maybe have several small enough to carry around in a backpack.
• cheap: at least, cheaper than what it'd cost me to buy them imported.

So the questions are:

• What is the best material to build them from? Plastic, probably, but what kind? And it should be opaque, preferably in a non-garish color, possibly grey or brown.
• What would be the best way to draw the grids on them? I was thinking of either drawing them with permanent marker, or, if the material is plastic, etching the battlemats with a hot knife, perhaps only with a small cross at the corners of the squares like you see in the official printed mats of DnD. Obviously, this would be way harder with hexes, but for starters, I was only planning 1 inch squares.
• What are the best dimensions for a battle mat, especially thickness? I figured I can start with the 26 * 23 1/2 inches of the standard Chessex battlemat, but advice is welcomed.

Partial resolution
Today, I bought

• a few sheets of cardstock,
• a con-tact roll,

and got out my sharpies, a pencil and eraser, and a ruler. I penciled crosses on the intersection of each inch square, then re did them with the sharpie, then painted half of the first cardstock sheet with watercolors. I'm not a good painter, so it ended up less neat than I'd like, but I can practice. After it was dry, I laminated it with con-tact. Total cost? less than U$S 4, and a couple of hours well spent. I'm happy.

I might try other suggestions as these first attempts degrade. I just wanted to say that I'm very thankful for the suggestions.