There are playground safety standards - a lot of them, and many of them include retesting on a regular basis - especially where there are padding requirements.

Two examples of elements that might be helpful:

24th St Mini Park in San Francisco

Topher Delaney's San Diego Children's Hospital

With that budget it might be better to work on a colorful surrounding and an interesting wall for kids with a big open space that allows them to use their imagination and play.