switching nikon to sony help

So I'm torn between this move but I'd like to try out an a7iii or a9, and then make a move from there. I currently own a Nikon d810 and a d700 with an 85mm 1.4 and 24-70mm 2.8 both Nikkor glass. I am liking the a9 over the a7iii just for the extra features. Money is limited to what I get for my...