
Purchase a similar CAD application that looks, feels, and functions like AutoCAD. Research exactly what AutoCAD will be used for and see if this is a better option. Purchase AutoCAD LT 2012 for around $1k which is still AutoCAD, but with limited functionality. Since AutoCAD 2012 runs a steep $4k, I would suggest an alternative. They only sell the latest version, which is currently AutoCAD 2012. The only way to purchase AutoCAD legally is through an authorized reseller, which you can find on the Autodesk website. You'll find most people who use AutoCAD don't agree with this but there are alternatives.
Technically you never own AutoCAD, you're only really "leasing" it. And yes, you are correct, it's illegal to sell older versions of Autodesk products, which in turn makes it illegal to purchase older versions since it's clearly stated in the EULA.
The online activation has been in the recent years of Autodesk Licensing.