You should not need additional lighting if as stated you have good natural light, even for green screen. But if you are going to use green screen at night you will need additional lighting. I know you want to keep the price down but this is what I will be using for my green screen lighting for my night shows from now on.

https://www.amazon.com/gp/product/B015DYIQ94/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Along with a Home Depot light(as per Eddie's description) above for subject lighting.

Later,