I used in our school colored chromatic metallophons for babies (15 $) and plastic recorders (5$) for preparing young people of 16 years for the teacher training college. Even the smallest harmonics for 1.50$ would fit.
My best advice would be: buy a tuning fork, with this you can train your ear: practice all scales, all intervals singing the absolute and relative names, singing all kind of chords:
E.g you get the chamber tone a’ of 440 hertz you can interpolate all intervalls: singing doremi (A major or latido a minor)
practice domiso (triade of A,) ladomi (triade) of a minor etc.
Try to keep the pitch of a’ 440 in your short time memory while listening music or while singing a well known melody.
The benefit for all sight reading will be much bigger than any accompaniment.