My Aunts laptop just died on her, so I am going to help her back up her data and pick out a new laptop. There are a lot of choices as far as laptops go, so I wanted to get some recommendations for her.
What she wants:
$600 or less
Preferably 17 inch screen, but would also go with a 15 inch
She only uses it for the basics as far as web browsing, email, office, ect. She doesnt have a desktop, so this is her main computer. Weight / size is not a big issue though, mostly a desktop replacement.
I'm a big fan of the Dell Inspiron 17. In fact, that's that I'm currently using to type this response. I've had my Dell for almost 2 years and (knock on wood) haven't had a single issue with this machine and I bought it refurbished.
The one you've found on Costco will certainly do all the tasks your Aunt will be doing. Because of the screen size the battery that comes with the laptop will last 3.5 to 4 hours max. However, you mentioned this is more like a desktop replacement, so battery life may not bee an issue. If your Aunt plans on doing any traveling, I recommend getting the 12 cell battery, which I've gotten up to 9 hours running minimal tasks.
As far as price goes I think you're getting a good deal. I just spent a few moments on the Dell Outlet website trying to beat your price, but couldn't. And most on Dell's website come with Windows 8.
Bottom line, I think your Aunt would be happy with that laptop.