Since I absolutely despise ebay, and happen to own a Sirrus, I would go with the Sirrus! Very comfortable and fun to ride. Fine gravel and dirt paths shouldn't be a problem, or you could upgrade to maybe 32-35c tires for a little more cushion and "off-road" capabilities.

There is nothing wrong with online bikes, for the most part, but you need the few special tools and ability to properly assemble them. For most people, its better to spend the money on a quality name brand bike from a reputable bike shop. If you are going to ride it hard for 5 months, Might as well have a warranty and a bike shop to back it up!