I think that's probably an unanswerable question. There are questions about condition, and focal length - some are going to cost more than others.
My own opinion is coloured by what I expect of a lens. If you make a 20x16 print from a 5 x 4 negative, that's the same degree of enlargement as a 6x4 enprint from 35mm. How much difference will you see between lenses on a print that size?
Schneider's Symmars went from Symmar, through various iterations up to the Super Symmar XLs. My first LF lens was a Symmar made in the 1950s from the serial number. It was sharp enough for me not to need more. Yes, the coating wasn't up to modern multicoating, so more prone to flare if you didn't watch out, and probably lower contrast. On that point, Paul Strand had one of his uncoated lenses coated, and found he had to reduce his developing times to compensate for the higher contrast. Turning it round, use an uncoated or single coated lens and just up the developing time...
I have two Sironars, an N in 150mm and an S in 360mm focal lengths. The 360mm is BIG, HEAVY and not to be considered taking out so long as I have an alternative. For a high price, you may be paying for the covering power, useful if you use a lot of movements or want to use it on a larger format.
As to better - well, that depends on the question "better for what purpose"? I have a 355mm Commercial Ektar lens, as used by Karsh for portraiture on a 10x8 camera. I had it with me on one occasion when I met up with another forum member. He named it "the discus" because of its size. Lovely circular aperture for the bokeh, if that matters. But carry it around all day in a back pack when I have smaller and lighter alternatives - no thanks.
What I can say with certainty is that LF lenses aren't being made now, and prices will only go up in the foreseeable future. There's a web site by Kerry Thalman that has a page on "Future Classics" in LF lenses; one person said that that site single handedly doubled the price of the lenses it picked out. Spoiler - two Sironar S lenses in it (135mm and 150mm).
Ultimately, what I would pay is going to depend on what I can afford and how much I want one. And these days, I don't actually expect to see any technical improvement from a new/different lens. But more coverage and a lighter weight. (Coverage matters more to me as I use 5x4, 5x7 and 10x8 cameras.)