Hi RayandPaula, and welcome to the forum!
For stills, I use an
Opteka 77mm variable ND and step up rings for my smaller lenses. Sadly, it is no longer available. If I was buying a variable ND today, I would get an
UltraPro 77mm for $40.
Of course you can spend more for a
Singh Ray or
Fader ND, but, in my view, ordinarily mortals can't tell the difference between the UltraPro and a Singh Ray.
For motion pictures, when I have time to mess around with glass filters, I use a
$50 aIR-Matte A2 matte box and Cokin P compatible NDs like this
$15 set from Rainbowimaging.
Again, you can spend a lot more for matte boxes and filters, but this setup works just fine.
Hope this is helpful!
Bill
Hybrid Camera Revolution