No need to spend so much money. Just get a few place mats at the dollarstore around the corner and draw a 1-inch-grid on the (probably blank) backside with a non-erasable marker. Afterwards put in terrain and everything with wet-erase markers. I use mats like this in all my games, pathfinder and other systems.
We use a giant white board and rulers. We like it better than the grid and the dry erase markers can track monster hit points, draw in spell effects (wall of force, stinking cloud, etc), terrain (walls, etc).
For us it feels better and more free flowing without the grid. Just some food for thought. You can also buy whiteboard paper and put sheets of that right on your gaming table or a piece of plywood for a HUGE table area (which is what we have) so players can even track hit point/buffs and such right on the table where they sit.
Erasable whiteboard game mats are easy and cheap to make. Just get some foam core posterboard (a buck at a dollar store) some clear shelving paper (a few more bucks) and a sharpie marker (you probably already have one of these).
I cut eight 8x10" sections from a 20x30 inch foam core poster board, used a sharpie and a ruler to draw a 1" square grid on each one, covered them with the shelving paper and voila! portable stackable dry erase battle grid boards.
I also have a large sheet where I just printed out a 1" square grid onto a large sheet of paper (I did this at a Kinkos or Office Depot) and then covered in shelving paper. You can roll it up and put it in a packing tube to keep it from getting wrinkled. Works great. Cheap too.
For good quality dry erase, I echo the basic flip mat. It folds up and travels easily and is easy to clean off. I like to draw scenarios on it before hand, fold it up, then take it to the game. It holds the image well and yet cleans off later when needed and it won't wrinkle.
For a cheaper alternative, you can always get a $4 roll of gaming paper. This stuff is not sturdy--it's basically wrapping paper with a 1 inch square grid on it. But it's cheap -- it will cost the same, if not less, than the posterboard, shelving paper, and sharpie that Adamantine Dragon recommends (with all due props given to a good homemade idea) and requires much less work (and you could always glue the gaming paper to a sturdier surface if you so desire).