I know I've mentioned the $19 Dano Fab Chorus on these "cheap pedal" threads in the past. I'm not a chorus-holic so this does everything I need for electric and acoustic. But today I'm going to throw out the Behringer ADI21 acoustic preamp/DI. I got mine used for $20 at GC on a whim (but they are still just $33 new). It has a simulated tube preamp can be blended in to mellow out piezo quack. And while it doesn't have a dedicated feedback or notch filter, the sweepable mids work well for both tone shaping and feedback suppression. I've used with acoustic guitars, uke, and a mando with a cheap stick-on piezo.