Since we are talking hypothetical, specifically focusing on used, there are a LOT of possibilities. For this exercise, I will stick with some recommendations on what I think may be great values for exceptional, "statement" type speakers, if they become available to you locally. The good news is that most speakers in this price range are typically fairly large and a tough sell due to shipping, so bargains can be had quite often.
- Beveridge Model 3 - if you do a search in AK, you will certainly find my name associated to the vast majority of comments regarding this model. Of the various Bev models, this is the ONLY one I would recommend. The Model 2 may have sounded better, however, it was not as robust and they have failed over the years, not so with this model. This speaker is simply unlike anything else, "magical" in a way vs most other offerings. They are fairly rare/unknown, so can be had for much less than your price range, but you can use that savings to give them a much needed recap. The stat in this model, thus far, has not shown to need any sort of rebuild, unlike Quad/Martin Logan, etc.. An AKer recently went to great lengths to pick up a set of these, still waiting for his follow up rebuild thread.
- Dunlavy SC-IV - I have not heard these myself, but everything I have ever read is glowing. I keep these on my radar myself.
- Pioneer Elite TZ-9 : When Pioneer, like other major vendors, wants to release top end product, they can do it. The Elite series exudes quality all the way around. They are great, all around, do anything type speakers, but seem quite rare to find. This is a 4 ohm speaker.
- Large Tannoys - I have only had one set of 10" Golds, but they left an impression. Probably not something to be found often within your budget, but it can certainly happen. The key here is finding some in nice cabinets.
There are certainly nice offerings from ADS, Klipsch, JBL, etc. but most of them are fairly common or outside of your budget in many cases.