How cheap does cheap need to be ?
How about the flash , the BY18 can be had for $10USD , and how much is a used drink cup ? ( This one came VIA Hungry Jacks )

Just cut the bottom off the cup so that it snugly fits over the flash ..
Then point the cup down to where you need light ( On the subject )
And tape the cup in place after installing fresh batteries ..

The resulting picture of the mantis is with the pictured flash unit .
Just remember , you could use a longer cup if you needed to direct the light more ..
Or use a wider cup with a lid if you needed say more of a diffused light .
Your imagination is your road block ..

Be happy , take photos , and don't forget to share ...

[HYS]

O-o! This cup is producing so nice pictures ...!

[Not a Number]

and how much is a used drink cup ?

Nothing if you do some rubbish bin diving.

And you could add more diffusion with a paper serviette over the mouth of the cup or maybe even wadded up inside.

Well done!

[BigMackCam]

Great idea

You could even make a honeycomb for the front by punching holes in a cheeseburger. On second thought, that's probably not a good move... greasy...

[bigfoxkiB]

This is a great idea...glad I did not buy a macro flash yet...

[old4570]

Nothing if you do some rubbish bin diving.

And you could add more diffusion with a paper serviette over the mouth of the cup or maybe even wadded up inside.

Well done!

I was thinking more along the lines of ( When you buy Take Away - take the cup home and wash it )

[Drake012]

Don't throw the white lid. It is a good diffuser.

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[old4570]

Yep - The lids make great diffusers !
My Metz flash has a drink cup + Lid ...