First, there are a few sites that have pre-owned wedding dresses for sale if you really want one of the two dresses you linked. I can't remember all of them off the top of my head, but from what I can remember, preownedweddingdresses.com, stillwhite.com, and nearlynewlywed.com are all legitimate sites. You can also keep an eye on general clothing resale sites like poshmark or even eBay and use PayPal to purchase them so you have a little extra protection if the dress received isn't what was advertised.
I would call this sort of style a "short high-low" dress. When I put those terms into google and filtered by white on the sites themselves, I found a few at the links below. If you're not a fan of any of them, just know this isn't exhaustive!! You've picked a very versatile style!
Not so sure about the quality of those Amazon ones, but like anything, just make sure you read the reviews and if nothing else, Amazon usually has a pretty good return policy!