I have not read all the posts so if I'm duplicating a post I apologize.
I bought on ebay for about $35.00 a kit that will run an old laptop monitor. It is a board that has hdmi in and has a cable that connects directly to the lcd screen. A 15 pin flat connector. The board also drives a smaller board that supplies the high voltage for the monitor.
HDMI VGA 2AV LCD Controller Driver Board 5 Keys Keyboard Kit for LCD Panel | eBay
7 inch LCD Screen Display Monitor for Raspberry Pi Driver Board HDMI VGA 2AV | eBay
Also available is a 7" lcd hdmi monitor and control boards. About $50 for 800 x 480 and $75.00 for 1280 x 800.
7 inch LCD Screen Display Monitor for Raspberry Pi Driver Board HDMI VGA 2AV | eBay
If you order the kit for a lcd screen you already have you need to find the numbers on the back and send them to the vendor. The high voltage board is different for some lcd screens.
I got a 1280 x 800 and that is too much detail for a 7 in monitor. Too small. The 800 x 480 would likely be better.
Larry