I got Tilecrest Montecito tile in an off-white crackle for $6/sq.ft. They also have white and non-crackle finishes. I know many others have used basic Lowes or HD white subways.

The Tile Shop has a crackle subway in white and off-white for $8.99 SF. Nice basic tile. You can see it online. The Grazia Essenze tile is a little nicer (meaning looks slightly more hand made and comes in a 2.5x5 size) and costs a little more -- not sure if it is under or over $10.

Am looking forward to seeing others' responses.

I got bella luna subway (travertine) for less than $5 a square foot. Someday I'll have to take a better photo of it. There are more photos in the album.

I am looking for a classic 3x6 white.

How about American Olean gloss white 3x6 subway tile for a mere $2.00/sf ($0.25 per tile) at Lowe's?

I don't believe that thicker tile is of benefit on a backsplash. If you want to mix with other tiles (accent) you would need to be sure the thickness won't be an issue.

American Olean for under $2/sft at Lowes! Love it. I used it for my very first DIY tile job in my bathroom and it turned out splendidly. Lovely classic white glossy subway tile. It's not beveled, but also not completely flat. Great shine. And they carry a zillion trim pieces, both in stock and special order, so you can really customize the look to fit your space. Very similar brands are DalTile and the US Tile at Home Depot.

For a tad more $$, I believe Lanka Tile makes a fairly affordable beveled white subway.

Circuspeanut is right. I used beveled Lanka white subway tile. It cost less than $6 per square foot and looks great.

Dal tile

Here is a link that might be useful: daltile

I just finished installing my first DIY tile backsplash with Lowes American Olean (but I used the biscuit color) and it was so easy to work with. If you want small grout lines like I did, it has built in spacers on the sides so you don't have to fuss with the plastic spacers....It was easy to cut and looks great and the plain white is $2/sq ft!