I often use transparent boxes made for foodstuffs or other household things (sorry, I don't know many correct household terms 
They come in all sizes and qualities. They have two drawbacks:
- many are much too "floppy"
- they are rarely rectangular
The trick is to use them upside down: I screw or glue a work plate onto the top, and close it with the transparent main part.
The work plate can be a strip board e.g.; epoxyd is much better for this than pertinax.
The boxes I use are between $2 and $5... But they do come in all sizes !