Hello all, I would like to get some advice if possible

I am looking to get a small waterproof box printed with internal dimensions of 120mm x 50mm x 26mm.

The box needs to be sturdy enough to not collapse if you put some weight on it but doesn't need to withstand being run over or anything.

You should be able to open it easily without the use of tools.

The box will be sliding into a tight fitting dense foam cavity so protruding clasps and the like are not ideal.

I am looking for any ideas to get me started on the design (mainly how the lid can be constructed to make the box waterproof with the above specifications). I would also like to know how much this would cost (in Australia) both for a one off and for production of many.

Any help is greatly appreciated.

Thanks