I was wondering if anyone has a favorite cheap (<$300) headphone amp ? Grado SR80's, which I have been using since high school, are my cans of choice. I have heard that running on battery power is sonically 'cleaner' than AC so I've a car battery and an inverter ready for a cheap upgrade to whatever I end up buying... TIA!
I bought an Antique sound lab tubes headphone amp on audiogon, used, around $200, i love it, another maybe more expensive choice, go with a benchmark dac which has headphone jacks, you will get a massive improvement in digital playback and a headphone amp
Grado actually makes a headphone amp that is powered by a single 9v battery that might be perfect. I listened to it a number of times with the SR80 headphones and it is much better than any headphone output that's built into a component that I have tried. Perhaps that should be on your list of products to audition. It's a bit above your stated budget, but worth a listen. Project also makes a nice affordable headphone amp.
It might be a little overwhelming at first but the Head-fi forum has way too much information about this kind of stuff and way too many people willing to give advice.
I ran my Grado RS-2's with the Grado RA-1 (9V powered) for a long time, and I liked them. Maybe look for a used one. But I now have a small collection of tube and SS amps. All unfortunately to my pocket book are all over your current price point.