Is there an affordable long run XLR preamp to amp cable out there?

I’m very happy with 25-foot cables made with Mogami W2549 and Neutrik XLRs, put together to order by Pro Audio LA. (I think the pair ran $105, including freight.) I recently auditioned some "audiophile" $2200 cables and they were not nearly as good sounding as the Mogami cable.

These run between preamp and amp in my system.

Tip: Most pro audio shops (including the one listed) can put red rings onto the XLRs of one cable for only a couple of bucks more.

Whatever Ralph and Victor recommend should work. They make differential balanced audio gear in the form of Atmasphere and BAT products.

Guitar Center stocks the Mogami Gold balanced cables (with Neutrik XLR jacks) in a lot of different lengths, 3ft. to 50ft ($39.95 to $109.95). A 25 footer is $69.95. That microphone cable is the standard in recording studios.

Van den Hull. That's what Pink Floyd used when they finally figured out that cables mattered. Don't know what model.
Atma-Sphere and BAT opinions are of little value unless you use their equipment.
But if you decide to try a pro cable also give DiMarzio a try. Yngwie Malmsteen uses it with his guitars. I tried RCAs only not XLR - OK but nothing special, ridiculously inadequate compared to some Purist and Tchernov that I have.

Atma-Sphere and BAT opinions are of little value unless you use their equipment.

That is not entirely true. Some high end cable manufacturers obtain Mogami wire and re-brand it. The wire is oxygen free and the dielectrics are polyethylene; pretty nice stuff. Overall its pretty inexpensive and thus totally worth a try. FWIW, Neutrik connectors are excellent; some of the best made.

Now the whole point of balanced operation is that the cable shouldn't be a big deal in the overall sound- its a system meant to eliminate interconnect cable artifact (in addition to ground loops). You'd think an audiophile would like that sort of thing- after all, it worked pretty well for all those recordings that people play on audio equipment :)   And some of those microphone signals had to go a long way!

So it is advantageous if the equipment supports the balanced standard. To my knowledge, this is a rare thing in high end audio so we have all these exotic balanced cables as a result. As far as I can tell the BAT stuff doesn't support the standard.