50 foot cables?

Thanks for all of this. I could potentially drill a hole under our floor, run them under floorboards and instead they'd be 25 feet. Worth that instead?

Yes, much better. I suggest DH Labs T-14 in your price range.

https://silversonic.com/products/bulk-wire-and-cable/bulk-speaker-cable/t-14-speaker-cable/

Next time you're upgrading, think about separates. Running long interconnects is less problematic than long speaker cables.

Hello,
With respect to your price range, I would highly recommend Belden 1313A speaker cable. This is a 10awg cable with oxygen-free copper and low capacitance and resistance, you should be able to go the whole 50'. I must admit though, that I am not familiar with Tube Amps. That said, for the distance you are trying to cover, this stuff should do the trick!

Good luck!