$300 for a new tri bike???
You gotta be kidding!!!!
Geez, maybe you can get a new rear wheel for a tri-bike for that price!
For $300, you won't even find a used bike that would be competitive. Maybe a used frame, or a well used component set, but that's about it!
Figure a minimum of $1500 for anything new that's even slightly competitive. Add another $150-200 for the pedals.