To be able to add friends on steam you need to be "premium" on steam, and as far as i know the only way is to spend 5$ on the platform, and the only way for you to add funds to your steam account is via gift cards, or by using a credit card since the Steam Community Market is also locked until you spend them 5$, sooooo there's not much you can do i'm affraid, maybe get someone you trust to give you a gift card in exchange for 2 or 3 of your TF2 keys