Buy a cyclocross bike. They're as tough (at least) as hybrids and very VERY nearly as fast as road bikes - in fact they're often used instead of road bikes for the rougher stages of road tours. They'll take wider tyres than a road bike and go off road. When you're ready for your triathlon you can fit aerobars.
If you're lucky you'll find a 2009 model Kona Jake on sale for $800.