That's a pretty basic model that you've provided a link to, but I'm sure it serves your purposes just fine. The higher end one is being sold at CostCo for $499 right now (reg. $699), which is still hefty, but you get a lifetime warranty when buying thru CostCo as long as you keep the receipt.
You can also buy refurbished ones on vitamix's website for a bargain, and they come with a five-year warranty.
The motor is the same so you're not paying more money for a better running motor. Some of them are more money because the base is stainless steel or you get a nicer carafe (or additional one).
I bought the basic model and have been pleased with it.
Oh and as far as Costco's return policy you can take it back and if you lose your receipt they can look up your purchase for you. Try and keep in mind when/how long ago you purchased the item so it makes their search a little easier.
More than likely, without a receipt you'll get a store credit which is better than nothing at all. I'm fine with this since I shop there weekly without fail.
Membership has its privileges.