Good mouse for 20 USD or less?

Here.

http://www.amazon.com/E-3lue-EMS109BK-Precision-Control-1600dpi/dp/B005CPGHAA/ref=sr_1_3?ie=UTF8&qid=1378252419&sr=8-3&keywords=mouse

http://www.amazon.com/Mazer-2500DPI-Optical-Black-Gray-EMS140/dp/B0095ONNTC/ref=pd_cp_pc_1

If you're ok with buying from ebay, there's nothing better than the Microsoft Wheel Mouse Optical

A4Tech X7 Laser. I have one and I Love it.

You can maybe try Logitech G100?

Do yourself a favor and wait for more budget.

I love this one

do you have access to a microcenter? They have really good prices on non-name brand stuff.

This one. I bought it several months ago and works very good.

G100S

I tend to be pretty rough on mice, going through about 1 a year or so. My current one is a Logitech M510 and it's lasted 2.5 years maybe and still going strong. They seem to go for around $30 on Amazon though, so a little more than what you're looking to spend. I got mine new via eBay for less than that, so a little patience and auction sniping might pay off.

http://www.amazon.com/Logitech-910-001822-M510-Wireless-Mouse/dp/B003NR57BY

Wireless Logitech mice with the two buttons near the thumb are great. I try to keep a spare around with batteries already installed so I can just flick the power switch on it and be running immediately. Great for when you forget to check your batteries before a heavy evening of online gaming.

You can find them on sale at Walmart for 14.99 USD or less.

I use this but it's $30 on amazon

Check these, i bought that V7 in 19.5$, they are so damn stylo and very good for gaming and normal use.
Sorry i dont now how to make it clicky..
http://www.bloody.tw/en/products.asp?cid=1

Logitech g400 its fit for the price

• Logitech Corded Mouse M500
• Microsoft Comfort Mouse 6000

Although these are listed as $30 mice on the manufacturers websites, they often retail for $20 or less.
Both are really good and comfortable wired mice with enough buttons for gaming and a good scrollwheel.

And if you happen to come across them at a bargain (they don't make them any more) I'd also recommend :

• Logitech MX410
• Microsoft IntelliMouse Explorer 3.0
• Microsoft IntelliMouse Explorer 4.0

i ve got this its pretty awesome but it cost a little more than 20$ :( bought it year ago

G400 if you can find it cheap enough.

this

Logitech M100 is an excellent mouse!

A4Tech XL-740K or XL-747H. It's durable and really really good.

This mouse can really make a difference from the cheap ones. It will move very smoothly and it kind of makes you think you have more FPS in games. It moves so smooth that games will seem to be running with more FPS. Cheap mouses stutter and make small jumps between positions on the screen.

It also comes with weights, a software with macro support and more. It's cheap too, especially for the quality. Even though I couldn't find it on Amazon I suggest you read some reviews and maybe choose A4Tech.

I just buy the cheapest Logitech or Genius mouse there is, they are usually around 7 $ here, they always work for 2-3 years before i have to replace them. I once got a 15 $ mouse and it broke after a year. Yea, i know im cheap, but that way i don't care much if it gets broken and i know it will eventually

I've been using this one for about 6 months now and it is comfortable and works well.
http://www.amazon.com/Gigabyte-High-Definition-Optical-Tracking-GM-M6800/dp/B003Y7MWZM/ref=sr_1_1