Hacks for noise reduction and acoustics for office space?

What are some low cost ways to improve acoustics in small office space? With concrete walls and just desks, the acoustics in our office are horrible. Everything echoes and it's hard to concentrate if anyone's talking.

Ideally you need two sorts of objects:

1) things which absorb sound waves: Curtains. Rugs. Large lamps. Chairs etc.

2) a reduction in the amount of purely horizontal and vertical hard surfaces. Adding things like framed pictures, which are hung a few degrees from vertical, will help to deflect sound waves instead of bouncing them from one hard surface to another.

The cheapest option: a white noise generator. You can either buy a dedicated one on Amazon for like $50 or you can just have a computer play a white noise mp3 in a loop.

Another low cost option: more furniture that's made of materials that will absorb sound. This would include sofas, curtains, rugs, etc.

Next best option: acoustic panels. If you can't afford to get enough for the space, you can check YouTube for videos on how to make your own.