I'm not cheap, but I LOVE this one for portable use and it's only $60 shipped with a no frills connecting cable (I don't use it , but it's OK) and a charger to charge the 2 AA rechargeables that you buy separately and put inside. I don't need anything better for use with a portable player. Would only spend more if I wanted one with a DAC to use with my computer. I wouldn't have felt over charged if I spend 4200 on it.
http://www.electric-avenues.com/audio8.htmlIt sounds great,
gets plenty of volume with high impedance phones like my Sennheiser HD650's (it has 2 internal L/R screws you can adjust for best combo of volume & sound with your phones) and lasts a long long time on a charge (supposedly about 100 hours with 2500 mAh rechargeables). It's quite small & solidly built, though not wafer thin. It easily fits in my shirt pocket velcroed to my Sansa e280.
It doesn't have any other features like cross-feed or bass adjustment, but you don't need any other features if you are using a Rockboxed player-you can adjust the sound in Rockbox.
Gary is very helpful if you have any questions, ships promptly, and offers a lifetime warranty if anything goes wrong. He has supposedly sold 6000+ of these things in the last 6-7 years. IMO he's the Chris Church of headphone amps. Comes from Canada too...