I also needed a swimsuit, and, at Nordstrom, in the swim department, I noticed long black skirts with elastic waistbands being sold as "dresses/skirts" for around $50. Took me a second, but I realized they were designed to be pulled up and worn either as strapless bathing suit cover-ups or as skirts over a suit. Hummm.
I remembered seeing something similar at Costco.
These matti m skirts at Costco are very similar, but sell for $16.99.
I'm not going to wear this to the formal dinner, I'm going to wear it over a swim suit. Probably.