<p>Just a few years ago, the idea that a 19-year-old from Romania had built a self-driving car would’ve sounded like science fiction. Now, to get attention, Ionut Alexandru Budisteanu had to do it on the cheap. While <span class="ticker_wrap">Google’s (<a class="ticker" data-symbol="GOOG" href="http://investing.businessweek.com/research/stocks/snapshot/snapshot.asp?ticker=GOOG">GOOG</a>)</span> autonomous driving vehicle costs $75,000, Budisteanu’s system—which uses 3D radar and a mounted camera to detect traffic lanes and curbs—can be had for $4,000.