A REAL Walmart Denali costs $159.00. Often on sale for $99.99. You say yours is "like" one. So, I will guess it is worth the same or less brand spanking new.

Perversely, decent bike parts cost more (often much, much more) than complete cheap bikes. You will have a hard time finding a replacement wheel for that bike that is less than the retail cost of the complete bike. Finding one that is not made of tin foil will be even harder. Finding one with a cassette installed that is not twice the cost of your bike is not going to happen. Not going through your local bike shop makes this project pointless. And, are we sure this bike has a cassette and not a freewheel? And that it is 700 and not 27" wheels? I have no idea, but have found that big box bikes tend to have odd part specs.

Buy a cheap but serviceable wheel on-line, buy a cassette, buy the right tool to install the cassette. Or consider the bike totaled. Or, maybe, just maybe go to a bike shop and see if they have any options that are better than the first two.

jim