Lane Bryant (www.lanebryant.com), www.torrid.com, www.alight.com, and www.avenue.com all offer plus-size clothing. On any of these sites, you will be able to buy an inexpensive plus-size evening gown.
You could try eBay.
It's easy to find find great deals on evening gowns and dresses on various sites, including Amazon, Ebay, and searching for various clearance events at local bridal and dress outlets.
in my ass
Many clothes stores like Debenhams sell evening gowns and websites like the chic fashionista can give advice as to where you could purchase them from.
The best place to buy a plus size evening dress for under $100 online is to shop at a store that specializes in plus size gowns. The highest rated store online is One Stop Plus (http://www.onestopplus.com) which has many evening dresses for under $100.
There are online stores that sell ball gowns. Simply dresses, Prom Dress Shop, Windsor Store, eDressMe, and Romantic Gowns are some online stores that offer ball gowns.
Visit the webpage www.edressme.com/. This site offers nice evening dresses and designs, as well as very acceptable prices.
While it may be advisable to find specialty stores that carry red evening gowns, it would be a lot easier to use a website such as PromGirl, this is also an easier way to get more inspiration and ideas about what is available on the market. Otherwise, store's such as Macy's and Nordstrom generally carry evening gowns in their stores.
Princess Auto online.
There are several websites that sell inexpensive evening wear. One is Discount Dress Up and they offer free shipping over $50 with the code at the top of their site. They have dresses separated by types and prices to make it easier to find what you're looking for. http://www.discountdressup.com/
Chances are you can find exactly what you are looking for by looking on the website craigslist or ebay. There are many companies and businesses selling inexpensive RV's online.
To buy an inexpensive sandbox online one of the least inexpensive is Walmart online. Another place is Target but it seems to be more expensive there but of better quality.