Electric Car
My Saturn has at most, another 8 years in it, probably closer to 5. This means I could take on an electric car conversion after the Earthship and have plenty of time.
The base concept is simple (and the devil in the details). Buy a car whose engine is shot but frame is in good shape. Rip out the engine and put in an electric motor. Have the motor interface with the transmission (skipping a few dozen important details) and you're done.
As a hypothetical, a classic Beetle had a 50hp engine. A 50hp electric motor goes for roughly $350 on eBay. I should be able to get a Beetle with a decent frame for under $1k, batteries for another $1k, chalk up another $1k for parts and finally, $1k for tools. I've got a working electric car and the tools to keep it running for <$5k.