Well I get awesome easy harmonic feedback from my Seymour Duncan 59s, they were only £120, thats 200 dollars, which is really cheap. You just pick a note, on a distorted channel, then sit back as it slowly turns to an amazing feedback tone.

Also using a wah wah pedal increases feedback but its often too sharp and ugly.

I dont stand too close to the amp. Good feedback comes with higher volume and the right ddistance from the amp.