I would have trouble living with the internal screen while editing some of my Excel files, and I also like the external screen for looking at Maps. I would not be without the external screen for home use.
Based on recommendations here on TidBITS, I have an Acer H277HU, perhaps six years old. (I bought it when I was using a MacBook.) It does not match the Retina display, but I don’t do serious graphic things and I don’t consider it deficient. For what it’s worth, I believe I paid almost as much for it as @Simon quoted for the Dell.
Still based on recommendation here on TidBITS, I connect a VAVA USB hub to the MBA and then connect all sorts of USB things to the VAVA hub and connect the Acer display using an HDMI cable. It works for me. I used to connect a MacBook to the Acer display’s USB-C port, but I had some difficulty and a nice person here on TidBITS pointed me toward the VAVA hub.
Huh. I hadn’t even thought of that. Let me know what you find.