I personally would get a tank made, and set it up your self, it is far more fun to do it that way.
When I bought a new glass tank last september it cost me $230 for 1.2long*.45wide*.55high (just under 300l), in 10mm glass, and I doubt the price for tanks has changed much since then.
I dont know much about floor strength, but 300l tank should be fine, as long as you dont go for a really high option.
I personally wouldnt buy a second hand tank, the saving in money isnt worth having 200+L of water and fish spilling all over my floor.
You should be able to get a tank of similar size set up for less then $800, but I personally think you should set one up yourself as it is fun, and good experience for when you set up more bigger tanks (or maybe it is just me that has mts....).
But I wish you luck on your endeavors.
:smot: but what are the fish that you have in your tank?