You can find some good bargains at thrift shops...heck it's where I got my 2nd monitor for my PC...$20 for a 22'' monitor? That's less than $1 an inch!
Fleamarkets can be even better at times, especially if they're a weekend only kind (bi-annually type ones) and the vendors jsut wanna get rid of their stuff on the last day...can score some sweet deals, even some nice free stuff.
There's a local thrift store called "ReStore" that gets donated stuff, all their proceeds go towards Habitat for Humanity...so you get a good deal and you're cash is going to a good cause, win win!