Boy, this is a tough one (used carbon or new entry level). I think if you find a great used carbon bike, and it's in your budget, AND IT FITS YOU, then you should get it. There's a chance it will be exactly what you want. If you get an entry level new bike, you're going to have issues with the components if you get more into racing, and either want to replace them or the whole bike really soon.

If it's for racing and tris, I think you'd want carbon.