Like most things the tube amp and the tube itself is a synergistic creation - just because an amp uses a cheap tube doesn't mean the tube is bad - it is VERY VERY possible and even likely that a high quality tube amp with cheap $6 tubes will sound much better than a cheaper tube amp using the most expensive tubes.

The Tube Amp comes down to design and parts quality - the quality of the transformers are more than half the battle, capacitors, resisters, volume pots, wiring.

What I would suggest is buying a few different inexpensive tubes from different makers and try them and see what kind of impact that has - just because it's expensive doesn't mean it's going to be better - it can be - but it can also be priced high due to limited numbers or rarity if it is a N.O.S. tube.

Incidentally the Chinese tubes are getting some very good reviews - just like their tube amps

Standard Shuguang Tubes
Sino Chinese Tubes

Although as Fred points out the 300Bs are not up with the best Western Electric - though those tend to cost multiples the price as well Shuguang Treasure 300B vacuum tube Review - Equipment Reviews - Dagogo

12ax7
TJ Full Music Carbon Plate 300B Getting to the heart and soul of the performance. Review By Leonard Norwitz

I think I am in more of the 211 camp than the 300B camp as well if I had the choice.