TomTop offers this NUX GP-1 Electric Guitar Plug Mini Headphone Amp for $13.99 with free shipping. That's $10 off list price and the lowest price we could find. It features a compact and light-weight design, built-in distortion effect, level, tone, and gain adjuster, and 0.25-inch plug. Requires two AAA batteries; not included. Note: Not in a rush? Opt to have this item ship from China (may take up to 3 weeks to arrive) to cut the price to $10.99.
There are lots of things Uncle Sam can't touch — so long as you play by the rules.