Finding a monitor for a raspberry pi can be pretty difficult if you are low budget. It is the most expensive piece on the whole cake. My first suggestion is to look at a local thrift store to and see if they have anything. Just make sure it works before you buy. If you want a new monitor here are my suggestions.
#1 10.1 Inch Small Monitor, Raspberry Pi Monitor Built-in Speakers
$65.99
This is one of the cheapest biggest monitors that you are going to find on amazon.

The rest on the monitors that are available are 7-5 inches. I am not sure If you will want them but I’ll show you anyway.
#2 HMTECH 7 Inch Raspberry Pi Screen 800×480 HDMI Portable Monitor
$65.99
This monitor is 7 inches and is the same price as the first one, and it is portable!

#3 Padarsey 5 inch Touch Screen 800×480 TFT LCD Display
$42.99
This 5 inch monitor is one of the cheapest that you can find. Meant to go on the older pi’s so don’t buy if you have a 4.

You can always find other monitors in different places. This post was referring to cheap amazon monitors. That’s all on finding a monitor!