I have had a portable headphone amp, the FiiO E6, for two years and eight months.
https://www.amazon.com/E6-Portable-Audio-Headphone-Amplifier/dp/B005HJWWW8
I think it's starting to go out on me.
Time to buy a new amp! 
I'd like to spend about $30 or less.
It has to be USB powered, it has to have volume control, and I would like it to last longer than my current model.
What should I get?
Do you need the portable amp form or you’re ok with desktop type?
Can’t really avoid fiio if you’re on a budget
Fiio A1 or the K1 is within your reach. I like the K1 due to the DAC feature but it is just that. The K1 has no battery pack in it.
There are quite a number of chinese amp out there that will drive well with no noise. Just that the sound you get is a gamble like any chinese product with no brands
I want a portable amp.
The FiiO A1 looks good, and the price is right.
Alright, I did research on Amazon, and the FiiO A1 looks the best.
(That's not too surprising since it's basically a newer version of the E6.)
I have read that the A1 doesn't amplify very much, but I don't need it to do so.
Looks like I'm set. 
What kind of headphones do you have that you expect adding another device in the signal chain is going to improve the output 
?
My headphones are JVC HA-S680's:
https://www.amazon.com/JVC-HA-S680-W-White-phone-Japan/dp/B00FS0DFTK
I'm not trying to improve the sound quality.
I just need to increase the volume somewhat.
EDIT: I have desktop speakers hooked up to my TV, and the volume going to the headphone jack is anemic.