I want to buy use the cheapest ever rubber track source to make my treaded robot. Will cycle tires work? But I want small.
Something like (bicycle tires, likely) that could work, but it would still require a bit of fabrication; for instance, you would need a way to remove the beads and sidewalls of the tire, leaving just a relatively "flat" tread, then you would need some way to either punch holes in the tread (for a direct sprocket drive) or some way to attach cleats on the inner surface of the tread. You would have to space them such that they fit whatever sprockets you are planning to use (or design and fabricate sprockets to fit).
You really don't have many options; there are rubber track manufacturers, but they are generally meant for heavy equipment and even the smallest would be too large for your needs (ie, small ride-on excavators and dozers). Another possibility, but still likely too large, are tracks meant for snowmobiles (also called snow machines).
You may need to go with a completely custom design. On possibility would be to use toothed cog belts flipped "inside-out" (for instance, timing belts that are used on car engines would be a possibility). Driving them could be a chore, though (maybe a toothed "idler" sprocket pulley in-between the idler wheels driving the top-side of the belt?); dirt would also be an issue.
You could always go completely homebrew; plenty of the projects at this site deal with building custom tracks:http://www.rctankcombat.com/tanks/
...it isn't easy, though, and may not be any cheaper than other methods. Most companies who design such tracked machines, design their belts custom as well, then outsource the manufacturing of them. I don't know if the company you linked the picture from does this, but they might. Then again, maybe there's a custom, small project cogged-drive belt manufacturer out there that does these kinds of things...
Finally - have you thought about forgoing a belt altogether? In many cases, a 6 or 8 (or more) wheeled design can be nearly as effective as a tracked design, and much simpler to design and source parts for...