And they are worth every penny.
In my dim and barely remembered past, I have used any number of products of lesser cost. But after using the top tier paints and varnishes, I have learned that using the cheap stuff is a mistake. The good stuff goes on like thick cream (paint) or honey (varnish). And it self-levels to a mirror finish. If you want to get a wonderful look, don't use the cheap stuff.
Recently, in a move motivated perhaps by ease of consumer clean-up, there have appeared in the marine market a collection of water-based products. These are made by withholding the normal volatile solvents carefully calibrated to give good flow properties on brush application, followed by self-leveling that stops short of sags and runs, and instead emulsifying the neat varnish resin in water. (For a familiar example, milk is an emulsion of milk fat in water.)
In the interests of science, I tried some water-based varnish. I can report that the product indeed looks like milk, and goes on just as if you were painting with milk. It is thin and runny, meaning that it would have taken perhaps three coats to be the equal of one coat of its oil-based cousin. It was difficult to control on a vertical surface (painting with milk...). And no surprise here, it raised the grain of the wood, badly.
But my biggest complaint occurred with use on a previously-varnished surface. After fighting the poor application characteristics, the final cured film was not adhered to the underlying surface. At all. I was able to use a fingernail to puncture the film and then lift it off in large sheets. I ended up removing the whole job and re-doing in oil-based material.
I cannot in good conscience recommend water-based varnish. In fact, my feelings are stronger than this - I strongly recommend against its use.
Perhaps one of you readers out there has had better luck with water-based materials? If so, I look forward to hearing about it in the comments. But fair warning: if you have never used the $50/quart oil-based materials, your experience does not count for much.