You won't find glass aquariums online unless it's very small ones. Shipping is way too expensive because of the breakage risk. It could easily cost $200 to $300 to ship even a smallish glass tank which means you can buy it much cheaper at the store.
EBay?
i would just do a google. i got my jewel 180 glass aquarium and stand for a bit cheaper than in petsathome. Postage included. Just search for aquariums and pet shops online etc. usually some good deals. But you can probably also get the same deals from shops like pets at home, who may charge less for delivery