If I were to build a budget system all over again from scratch, there are only 3 options I would consider, in two categories.
For locking myself down and preventing myself from upgrading for a long time, I would go with pro studio powered monitors. Specifically, the event tr-5. I spent 8-10 hours listening to various monitors from $300 to $1400 and on the cheap end, these are IT. I hear things about the yorkville monitors (canadian monitors,) but those are closer to $400 used or on sale. I also didn't get to hear them, so who knows if what people say about them is true. Going this route locks down your speakers and power amp so you can't frivolously upgrade as easily as you otherwise could. And BOY do those events sound good! Go to your local guitar center to hear them.
Otherwise, my two choices are the powerwave for some efficient speakers or a panasonic digital amp like the xr-25/45/50/70 for less efficient speakers. The first two are discontinued. Now keep in mind I haven't heard these, but people I trust say that they are awesome. Many people have compared the powerwave ($100 poweramp) to el-34 amps costing over $1000-2000, and come away not necessarily saying that the powerwave lays down the smack, but that they are shocked at how close the powerwave comes. In some areas, like detail, the powerwave is also clearly more...detailed. This amp has been recommended by multiple horn speaker manufacturers now. They love it with horns. The panasonic amps also share a similar reputation. Some people may recommend cheaper regular analog amps like a cheap rotel, nad, etc...I don't buy it. Not with acoustic material, at least. I haven't heard a cheap normal amp that I liked.
There is an exception to this amp rule I have developed for myself. Some speakers are really amp INdependant. For example, my friend's dad has an old pair of JBL 3 way floorstanders that sound AMAZING. I don't remember the model. I've heard him run it off of all sorts of cheap amps. Currently it's running off an Onkyo receiver. These speakers are great! I would guess that if you were to be able to find these speakers at all on the used market, they would probably go for ~$200-300, but they seriously kick butt especially because they sound good off of cheap amplification. They're open sounding and throw a nice broad soundstage, though it's not the most razor sharp imaging I've heard. The only thing wrong with these speakers is that the 12" woofers use foam surrounds and one of them has torn on my friend's dad's speakers. Oh well, pretty cheap to fix. I think a better amp would probably wake the sleeping bass monster inside the cabinet too, but it already sounds "good enough for me." This option requres you to know what you're doing though. You have to be very familiar with the speakers you're buying.
