Training for 1st sprint... need bike advice please

Hi there,

I think I accidentally posted this in the wrong forum so I am re-posting it here in the "introduce yourself" section.  Hope that's okay!

This is my first post and I'm excited to introduce myself!  

I am 32 years old, female, mother of two little boys.  I've been an exclusive runner for a few years.  Most recently, I ran a half marathon in December and since then I've really just been burned out.  I still run 2 or 3 times a week but not the distances that I used to.  I also very recently added swimming and weight training to my exercise regime and I'm really enjoying the addition of something new!  

I have decided to train for and compete in a sprint triathlon at the beginning of September but I still need to buy a bike!  I know someone selling their Canondale R600 CAD bike and I was wondering if any of y'all had experience with this type of bike and knew what a fair price would be?  It's at least 5 years old. I know nothing about bikes and realize I have much to learn! Would that type of bike be okay for training for my first triathlon?  

Also, what does everyone think about training on your own vs. using a training company to help train you for your first triathlon?  Would love to hear any opinions!  Thank you so much!  

I'll try to post a pic of the bike I am considering buying here.....