What road bike is right for me?

[heatherjo]

Hi I'm a 17 year old girl and me, my sister, and my friend are riding from our house to the coast in massachussets this summer. We live in NY and its a 515 mile bike ride. Were taking bike paths but were going to be doing about 100 miles each day. I was just wondering if anyone could help me find a good road bike for this trip that is under $300. Also I am not interested in renting because I would like to start doing alot of trips. And if anyone knows a good training plan for this that would be lovely too! Thanks <3