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This is false to very large degree, you have simulations for robotics, and you can buy/build your self cheaper versions.

It is also likely even after you purchase a physical arm you'd prefer to use the simulation as the feedback loop is both testable and much faster.

What are some good open source simulators suitable for robotics development?

(preferably a physics simulator library, not an entire framework)

PyBullet (I guess Bullet more broadly) sees a lot of use