Hello and congrats on deciding to give this a try. I'm new to it myself, but absolutely hooked.
I don't have a wealth of experience to share, but I can offer a few tips on scoring a bike. First of all, don't be afraid of not having the "right" bike. Most of the "entry level" triathlons have people competing on everything from high dollar dedicated tri bikes to old road and mountain bikes and lower end bikes from Wall Mart. If it's reliable enough to finish the bike portion of the race, you can use it, and if you're reasonably adept at cycling, even hold your own against the "better" bikes. Some bolt on aero bars will allow you a better position, and are a cheap upgrade.
Depending on your budget, you can spend anywhere from a couple hundred dollars to several thousand on a bike. I've found some great deals on Ebay and Craigslist, though, with great used bikes selling for pennies on the dollar. A well cared for, older tri bike will serve you well and save you a small fortune, and I'd personally rather have a good bike with some scratches, and high end components, than to compromise on a lower end bike bought new. It'll also allow you to make your mistakes on something you won't cry over if it breaks, and if you're decent at buying/selling, you can break even if and when you upgrade
(or even make a few dollars
).
In the last couple months, I've picked up a Q Roo Kilo for $300
(which I used on my first tri
), a Cervelo P2K for $700
(with Hed wheels and a couple powertap hubs/power meters
), and I'm building up a P2SL frame with all Dura Ace components that I'll have about $700 into when I'm done. Patience is a virtue, and don't be afraid to wait for the right deal.