Mohannad13I don't believe you can find a <$100 Tube DAC/Amp combo. Even if you do, you will have to spend at least $30 more on a non-chinese replacement tube right out of the box.
I think you should look at some solid state combos under $100 such as FX Audio DAC-X6, SMSL M3, SMSL SD-793II DAC/Amp. Depends if you are after a Cirrus Logic or ESS Sabre DAC chip. I personally bought a thumb-drive based on ESS Sabre9018K2M chip DAC/amp that I will be able to plug into future Tube Amps (amps only).
DAC+Amp combo + 12AU7 Tube definitely exceeds a $100 budget from what I find, so the xDuoo TA-01 price seems very reasonable. Let's see how it sounds when it arrives.