Coaxial cable isn't going to do your job. You can run thin coaxial cable (10base2) upto 185 meters. Thick coaxial can go upto 500 meters, but is certainly not a good solutions.
If you are able to place a hub somewhere in between middle of the connection, let's say around 110-120 meters, you might be lucky and it might work.
There are also two more solutions, but more expensive. First one would be a fibre connection, which will work fine. Second and more practicle is a wireless connection which will require a line of sight, in other words, you need to be able to see the other side and not have any buildings in between as they will interfere.
Why not setup a wireless bridge? depending on your LOS and your antenna building skills you could get away with a full setup for <US$200 and that would avoid laying thick coax($$$)...depending on the equipment you choose and your SNR you can get speeds up to 54mbs(infact I think they've gone a bit higher now)..half duplex though.
Anyhow, best of luck, I just layed down 120m of cat5 and that was a pain in the asss...200 odd metres of thick coax would suck big time.