Psychotic neighbor and sneaky ex-husband – looking for recommendations on a home security system.

Hi! I’m hoping I can get some recommendations on a home security systems that are reasonably priced ranging from just cameras I can install myself to security system companies. Price is my main constraint, I was figuring to just get a couple cameras to install myself but open to going with a company if it’s reasonably priced and offers significantly more benefit. Thank you all for your thoughts!