I wonder how you would measure the right size of bike you would need. I am in the process of purchasing a bike (for commuting), and I wonder what size is most appropriate for me. I went down to my local bike store and they told me anything from 17" to 19" would be fine. Still I wonder if there is any accurate way to measure the right size of a bike I need. I am 5' 9".

Also, if there's any recommendation on what type of bike I should purchase I would appreciate it. I need a bike for commuting between home and school (a total of 5 miles both ways). This is urban commuting although the pavement is broken in certain parts of the city and there are hills that I have to climb. I am debating myself whether I should purchase a hybrid or a road bike. I am also leaning toward buying something that is not all that expensive, i.e., around $200, hopefully. Do you recommend that I should buy online (Craig's List, ebay, amazon, etc.), in local department stores, or at my local bike store?

Thanks much.