Instruments are expensive, especially the good ones. A bow for an upright bass or a violin can easily be found for $40,000 or more. A freaking bow.
Still, not having an instrument shouldn’t stop you from making music. Check out these guys playing on a broom guitar, and shovel bass.
Below are some more videos of people jamming on home-made instruments.
You can come up with percussion instruments, at the very least.
And that’s to say nothing of mental practice, practice away from your instrument. There’s a chapter on the techniques of mental practice in The Practice of Practice.