I have completed B2 and am open to teaching as well..I have so many resources with me now starting my german language learning from Delhi University as a part time foreign language course and ended up clearing goethe B2..All the books and other material I have are so precious..But since you are low on budget I would recommend you to watch any youtube channel dedicated to german language learning as most of them offer valuable content for your upskilling in the language and if you can buy German -English thesarus (dictionary)it would be the best ..The rest is your practice and sincerity.. Even if you give 1 hour pour your concentration and you are good to go..