Compared to the 185/50R16 size, the 195/45R16 size has an outside diameter that is a little bit smaller and the 195/50R16 size has an outside diameter that is a little bit bigger.Budget isn't really a problem. It was more to see what the difference was between the 3 different sizes? I.e. as you say, if 185/50 isn't available, then 195/50 is ok, but what are the differences?
The outside diameter of the 195/50R16 tyre is 1.7% bigger than the standard 185/50R16 size.
The outside diameter of the 195/45R16 tyre is 1.6% smaller than the standard 185/50R16 size.
Anything around 1.5% to 2% difference is often considered an acceptable difference.
If you want to try a different size to the standard 185/50R16 size, I would suggest 195/50R16 if using the standard 6Jx16 ET35 rims. 195/50R16 tyres will give you a noticeably better ride than the rather low profile 195/45R16 tyres due to the extra sidewall height.
195/50R16 has about the same outside diameter as the 185/60R15 size which is commonly used instead of the standard 175/60R15 size.
Another advantage to using 195/50R16 tyres instead of 185/50R16 tyres on the standard 6Jx16 ET35 rims, is that you get better rim protection from kerbing damage as the sidewalls will bulge out a little more. You would also get a little more protection from pothole damage due to the 5mm increase in sidewall height.