Since you're looking at grad ND filters, the Lee system is the best option…no way you'll get in for $100, though.
Can't afford the system?
By the filter by itself and hand hold, works fine and I have done it for years.
When you get the money buy the Lee System.
You know what. I am going to follow your advice with some modification. I'm gonna get a z pro holder and one Gnd filter. And then I'll tape it to my lens so that I don't have to get two adapters. This should be ok for now.
I have the lee holder, and often it is more trouble than it is worth.
There are several video tutorials on how to hand hold graduated filters. How to Hand Hold Grad ND Filters
This is just one. I have stacked them and held them for long exposures. The ability to put the graduated at different angles is an advantage of handholding. With a holder your stacked filters are in line. As long as you are aware that you need to keep your fingers out of the picture it works fine. Another advantage is the use of a CPL. You can hand hold over top of a mounted CPL.
Give it a try, the thing is if it doesn't work you, you have lost nothing. You had to buy the filter anyway.
My logic in a finance limited situation would be that I would rather have a high quality filter over a low quality filter and holder.