The cost isnt for the tank. The cost is mainly on the light and the filteration. Marine set-up are more difficult to keep. And their stuff cost more. A 65 watt powercompact light can range from 70-100 bucks.
the tank is really glass
and yes it has saltwater intentions and capabilities.. the filter is simply a run through or a 'sump" and the lighting is a dual PC that intense enought for soft corals..
you can use it for freshwater but i dont recommend it due to the filter design