Low powered flash recommendation?

[Steve-F]

Hope someone can help with a cheap option?

I occasionally find I'm shooting in low light with a fast lens (f1.8) and high ISO but just want a little bit of off camera flash to highlight my subject (I do want to keep some of the available light). I have an old Metz flash that's great for other situations but is way too strong for this .... and I can't dial it down - it's lowest setting is f4 at ISO200. I have a wireless trigger that works off the hot shoe.
I use both a Nikon DSLR and a Canon DSLR.

Thanks for any recommendations??

Steve.