Well, the first couple of months, the cheapo one will work fine. If you leave it out all winter, it will be a rust bucket come spring. The biggest advantage to the Weber is that it is going to last longer. The second advantage is the easy access to repair parts like grates. The 3rd advantage is the better customer service.
I have learned the hard way on a lot of different kinds of items. If you buy something cheap (cars, appliances, cameras, electronics, tools, watches, etc.) the item may work well for a week, a month, or a year... But eventually that item tends to break down long before the usefulness that would have been achieved by buying quality from the start.
In other words, you save money in the long run by buying quality up front and then not having to repair or replace as often.
Just my $0.02.