Scott Elder at Planet Analog describes how to Design a Custom Analog IC in Your Garage. Most of the tools are free or very inexpensive ($100). The fab cost is around $3000 and the packaging cost is around $1000 for 10 packaged parts. The tools can be found at:

• LTSpice
• MAGIC VLSI Layout Editor
• Electric
• Fedora Electronics Lab
• juspertor layout editor