Start cheap - you may do a couple of sprint tris, decide it's not your bag and end up with a £1K bike you use once per month to go work when its dry.
Here's the deal
- spend £400 on entry level bike and you enjoy triathlon - you'll want to upgrade.
- spend £1500 on a mid-level bike and you enjoy triathlon - you'll want to upgrade.
So get a cheap functional built proof bike, fit mud guards if that's your thing - personally I'm unsociable and don't.
In a year's time it will either be gathering dust or sitting on a turbo whilst your new shiny bike becomes your pride and joy.
Whilst a lovely expensive bike is nice to have, its certainly not required. I averaged 20mph at IM Switzerland on an aluminum ill fitting road bike costing less than £400.
Sometimes its better to look like a novice rather than a prick with a flash bike that doesn't need it.
*yours having a new flash bike being built as I type - but I'm a prick