Tihab, I'm another person with the view that given the length of the trip, it's worth spending the extra money on a very good quality new tent that has a known track record.
the other major factor is all the day to day practical stuff, ease of putting up, taking down, space inside, door placement, shape etc for strong winds..... but if you've never camped much, it may be hard to evaluate these things.

all I can say is that with day after day camping, you appreciate a well designed, well working tent, and totally worth the extra money compared to a "deal" on a used tent.
so many good new options, and by simply not staying in a motel a few times or not buying stuff you don't need, the saved money would cover the cost of a well chosen new tent.

also, a good tent will get used for years if using common sense with taking care of it.... again, no idea how much camping experience you have.

oh, and for a long trip, 2 person tents are ideal for person just because of the space for your stuff inside, for days off etc, worth the extra bit of weight imo.