In addition to brackets also consider hinges [1], like the standard 1x2 hinge [2] or for higher load a combination of e.g. [3] and [4]. There are also various solutions using Technic parts.

I'd honestly just order what you need from bricklink. Alternatively get used Lego by weight from ebay. Around here you get a kilogram of unsorted, good quality Lego for €20.

1: https://www.bricklink.com/catalogList.asp?catType=P&catID=22

2: https://www.bricklink.com/v2/catalog/catalogitem.page?P=3937...

3: https://www.bricklink.com/v2/catalog/catalogitem.page?P=3036...

4: https://www.bricklink.com/v2/catalog/catalogitem.page?P=3038...