Don't bother to get a special and expensive TT bike to start on - if you don't go fast it will only be an embarassment.
The majority of TT riders are rarely in contention to win events, so most of the time they are aiming to improve their own times. In this context allowing yourself time to progress to the best equipment should give more scope for p.b.'s and so prolong your interest.
If possible, do some road racing. This should improve your speed, but more importantly may ward off the staleness and boredom which often come from riding too many time trials.
The majority of TT riders are rarely in contention to win events, so most of the time they are aiming to improve their own times. In this context allowing yourself time to progress to the best equipment should give more scope for p.b.'s and so prolong your interest.