I think a large tank is relative to what kind of fish you are keeping, a 55 is large for a moderate colony of guppies but somewhat small for large haplochromis from Lake Malawi. I like to look at aquariums based on dimensions and inhabitants rather than gallons, giving them plenty of room to swim around (or swim away from one another) and how those fish fit into a tank. I think nowadays anything under a 30 gallon is considered "smaller", 30-75 gallons is considered medium, and anything above a 75 is considered "larger" but again would depend on what you are keeping.
Thats a bummer to hear that glass constructed tanks are so expensive where you are from, have you considered setting up some plastic tote containers? I use these all the time for quarantining and raising fry. They are light, easy to disinfect and can stacked together so storing them is a lot easier. Just a thought.