There are hacked versions of ACAD around which cannot possibly be
recommended. Or you could try autosketch?

Somebody I know got into serious trouble at work having got a no dongle
version of ACAD 2000 off the net, along with a dogy serial number. Not
recommended. Full AutoCAD is around £3000 but the LT version can be got for
around £500. If you have a serious interest and are not short of a few bob
the LT version might be a possibility. It is not that difficult to learn the
basics.

Eric