I have a 4-camera setup that cost less than $150.
The cameras are very cheap -around $25.
Just get the box it goes into, plug everything in and done.
Many don’t have hard drives in them, but those aren’t pricey.
My last one and current one sends the signal for the cameras to my iPhone anytime I click the app.
There’s far too many brands to name. I’d suggest looking at the ones with the best reviews.
Would you PM me a sample link of what you are talking about?