Where can i find a cheap mp3 player for the car?

Not sure what your budget is so included a few for you to check out! I like the one's that have more then one feature.
JVC KDS23 Car Audio Player - CD-R, CD-RW - MP3, WMA, CD-DA - - AM, FM
Audio Accessories: Speakers - Media Format: MP3, CD-R - Features: Remote Control - Video Accessories: Presenters / Visualizers - General Audio & Video Accessories: Transmitters / Receivers
Additional Information: Features: Rotary Controller Multi-Control 24-Bit Resolution 1-Bit DAC Compu Play

You have three choices when it comes to playing mp3s in your car. The first option is to use a adapter kit to hook up your mp3 player to your cars radio.
Your 2nd option is to buy  a mp3 capable head unit..
3rd option is if you already have a mp3 capable head unit. You can burn all your music on to CDs as Jukebox Audio disks which allow you fit 200-300 songs on each disk.

The Pyle 2 band head unit has a front aux input that will allow you to hook up your mp3 player to it as long as you got a seperate 3.5mm stereo cable.
Or if you willing to spend a bit more money you can buy a used Panasonic Head unit for $85

If you currently don't own a portable mp3 player the Transcend's T.sonic 840 is inexpensive and is a great choice. The 3-phase wheel control and the intuitive graphic user interface make the player simple to use. Here are some of it's other features:

• 2 GB capacity for about 500 songs
• 30 hours of music playback on fully charged battery
• 1.8-inch TFT LCD screen with 176 x 220 pixel resolution
• Plays MP3, WMA, WMA-DRM10, and WAV audio formats; MTV video format (convert using included software); JPG and BMP image files