There are some cheap CNC routers. They often require a bit of setup (i.e. sold as kits) or have questionable quality (3020). I'm not sure you'll find a high quality solution under $500 though.

Shapeoko 3[1] is $1000 USD

X-Carve[2] kits are $800 (upgrade to the Shapeoko2)

3020 Clones[3] are around $500-800 (all over ebay)

[1]http://www.shapeoko.com

[2]https://www.inventables.com/technologies/x-carve

[3]http://www.aliexpress.com/wholesale?SearchText=3020+cnc+rout...