I prefer a lightweight cotton maxi dress, or I have some pretty cute covers from Target.
They're both a bit like this, fairly low cut, one is chocolate brown and the other is gray - empire waist, lower neckline, and the right length that they can be thrown on over shorts/capris like a tunic, or worn as a shorter dress.
Both of mine I wear the most are from Target. One is a linen "dress" with short sleeves and scoop neck. The other is a tube-like coverup with ruffles on the chest. Both work to wear at the beach and cover up enough to go to eat or run an errand afterwards.
Another target dress signing in. I also have a terry tube dress cover-up that I got at one of the million beach shops when we were on vacation one year.
Target or H&M. I have several dresses from H&M that I use as cover ups. I spent $10-15 on each and they look great and work perfectly. As a bonus--I can dress them up with jewelry and also wear them to casual dinners.
I happened to find a gem among the ones in Macy's for $20, so you might want to check the racks/webpage.
I do also own some pricier ones from Coolibar because they are pretty and UPF 50+. If you ever decide to spend a bit more and want good sun protection, I recommend them.