Agree with the above (all of it in fact), this really is something you need to research yourself.
There are such a wide range of tanks, from those that are
JUST a big glass box, all the way up to those that come complete with cabinet, hood, fancy tank shapes, filters, heaters, lighting....
The style of tank you want, what equipment you want with it, and what you want of the tank will ALL effect the price.
For instance, a 36 US Gal. Tank:
£25 36 US Gal.
£25
or slightly larger 47 us Gal. Tank
£420 47 US Gal.
£420
Ok, so the second one is slightly larger, but it's new, and it comes with all the gubbins.
So... only you can decide, this is why YOU need to do the research, there will be such a wide price range noone can really help you.