I love Nordstrom. Yes, they have some really expensive dresses, but they have a decent selection in your under $200 range as well. Free returns with no hassle and no time limit.
Your best bet for price-for-the-quality is to look at consignment stores. They can be hit or miss with sizing, but it's usually worth a look. I've had almost no luck at thrift stores, but consignment does a lot of culling so only the decent stuff makes it to the rack.
Also, if you have a Nordstrom's Rack near you, check that out. Likewise many TJ Maxx, Ross, and Marshalls stores will have formal wear. Often there is more formal stuff at the locations in more expensive neighborhoods.
If Crispy's dress doesn't work, or you want to look for back ups, those are all solid options. I buy most of my formals and cocktail dresses on ebay, but that only works if you have a brand and style that you feel confident will fit you well, since there are no returns (though you can resell anything that doesn't work.)
I've heard mixed reviews with Rent the Runway. If you are a standard size, it can be great, but you can't tailor anything so if you are short or busty or anything non-standard, it doesn't work well. Also, there's no margin for error. If the dresses (I believe they send you 2 sizes of the same dress) don't fit or you hate them, your even it tomorrow and you are screwed. Lastly, if it matters, RTR is very, very popular in the military world and it's not at all uncommon for there to be duplicates at the same event. Of course, that can happen with any dress, but given the popularity of RTR and the fairly limited selection (compared to all the formal gowns in the shopping world), it's much more common. To some people, that would be a big deal.
