I got a Targus bluetooth mouse (AMB04US) at $13. I prefer Bluetooth mouse as there’s no dongle that protrudes from my laptop (and frees up a USB port), but this means far fewer choices. The size of the mouse is 4.1″L x 2.1″W x 1.4″H (104.8mm x 54.4mm x 35.7mm). I’d say it’s medium size as according to this thread, Bluetooth mouses have length from 3.1″ to 4.9″. Dell 5-button Bluetooth travel mouse matte black looks great but it’s considerably more expensive at about $30 (3.75″ in length).
Usually it connects within a few seconds, and if it doesn’t it’s the bluetooth of my laptop not working and I have to switch it off and on again to have it working. The feedback when scrolling the wheel is not as strong as my other mouse, but it’s still way better those that scrolls continuously (I hate that), and I get used to it after a while.
It takes 2 AAA batteries and the batteries are good for at least 10 days for my light usage (I don’t care that much how long would the battery last as I’m using rechargeable ones). The LED will not switch itself off completely as opposed to my other mouse using 2.4Ghz (for which you can wake it up with a mouse click). The LED will fire more sparingly when not in use, though. When it’s low battery the scroll wheel will flash red. The DPI setting can be changed between 800 and 1600 DPI by pressing and holding the scroll wheel and the right button for 3 seconds.
I’m very satisfied with this mouse, and it’s one of the cheapest you can find on the web (It’s $10 on Amazon few days after I’ve bought it!).