New and confused

Welcome to this sport, and congratulations on finishing your first tri. 

If you're the kind of person who'll buy something and use it, and use it, and use it, you can do pretty well buying a bike in the price range you list.  Buy a bike. 

If you're the kind who's always buying, upgrading, upgrading, buy a bike.  You're going to upgrade in a year whether it's a $1200 bike or a $2200 bike and you'll want to upgrade even if it's a $3000 bike. 

Buying a used bike is OK if you know what you're looking for (specifically size) and are reasonably competent with a set of tools.  Keep in mind that a new bike comes with a warranty and the LBS should set it up so it fits you reasonably well (maybe not a full-fledged fit, but at least 10-15 minutes of eyeball-based adjustments) and cable/brake adjustments after it's broken in. 

I have been doing Tris for 2 years now.  Originally on my 1988 heavy road bike with clips on the pedals wearing my running shoes. Did a sprint and an Oly distance with that bike. 

I decided I loved tris and wanted to be able to have a shot at not getting dropped by the stud bike group that my husband and son ride with every week.  So... spent about $1000 on an older model road bike.  Got clipless pedals and bike shoes....rode on my trainer a lot over the winter and it made a HUGE difference.  I have added aero bars, and did and oly and half ironman last summer.  This summer am training for another HIM and for me personally I feel like I don't need any upgrade on this bike.

I don't feel the need for a tri bike because I ride with a group so often, and although I am competitive in my ag it is not like I am looking to go pro or anything.  I think we sometimes get caught up in the equipment, when what we really need to get better is to work at good technique and training.