Best tube-based phono stage?

It sounds like your pal is not into very expensive gear and I think the OM5 cart is MM. I would not go with tube and I love tubes for everything else. The permissible noise level for a phono stage is miniscule the best sounding tubes in terms of tone tend to be old stock which are getting very scarce as truly unused. Used tubes get noisier with some age or so it seems. My whole hearted suggestion from this all tube guy otherwise for about $450 is the Graham Slee Gram Amp 2SE. It is appropriate for MM or high output MC. the sound is far better than its relatively low cost would suggest.

I think given the cost constraints that a "good" tube phono stage will be hard to do. However there is another thread discussing the delight a couple of posters have with their Jolidas. New I think your still bumping up on your ceiling. Perhaps a used Jolida but no fancy tube rolling which is expensive and in my mind usually optimizes tube gear. (That thread likes the cheap tubes so it may not allways be needed.)
Thus again, for the money, I am telling you that you can't beat the Graham Amp Gram Amp 2SE. It is where to go and it is for MM.

Best of, for a specific price is usually readily discussed. I wouldn't be discouraged , and you have gottten some suggestions, but for clarity you might want to repost. You can be very specific as you already know the table costs about $500- $600. Thus all you need ask is for suggestions for a tubed phono stage for less than $500. I still think you'll get much more bang for your buck with SS, but there are many other choices. Good luck.