Good thought about a used saw. My old D8 rip saw was handed down through the family - belong first to one of my mother’s uncles who owned both Disston and Atkins saws - now in my shop.
I see older Disston hand saws from time to time at garage/estate sales - but some look to be more modern versions after the company was sold off. My understanding is that these 1960’s or 1970’s vintage Disston hand saws are nowhere near as good as the older ones. I also have seen some saws for sale with cracked or broken handles - but there are resources (patterns, applewood etc.) to help you restore/remake these. Missing teeth may be another issue - one or two may not be too bad if the price is right - but the old machines for re-toothing a saw may be hard to find.
As you point out - an old hand saw will probably need to have its teeth sharpened (perhaps jointed and set too) - and all the rip saws I know of seem to be easier than crosscut saws - because you can file them (probably as made in the factory) without introducing any fleam (although a few degrees of fleam will smooth out the cut).
Saw sharpening files are inexpensive (probably a 7 inch slim taper for a 5-1/2 or 6 point rip saw) , a saw vise can be made or bought and the learning curve for sharpening is not too steep.
Your link - shows that a good old rip saw might cost something like $200 and may be something like 26 to 28 inches long (I think Disston made ones from 22 to 30 inches) . My recommendation about Wenzloff - was made - thinking that it would work very well right out of the box. Learning to sharpen it - will still be a very useful skill.
I also thought that a shorter saw (20 inch) was more akin to modern thought on panel saw length and working a bit lower to the ground - although the extra length of the older saw may have the advantage of making straighter/easier cuts (letting the saw do the work as I was taught)