NTSC-only direct-view sets are already as cheap as they can be while still allowing the manufacturers to turn a profit on them. Are you sure you want to buy a nonHD-capable set this late in the game? (NTSC broadcasts will be halted in just a few years.)
First rule of electronics: the price will drop just after you bought it
On a more serious note I have to agree with Jack, it's getting to the point where I'm sure the glass in the tubes costs almost as much as they're selling the whole thing for... My prediction (if you can call it that given FCC regulations on the matter) is that within the next few years non-HD (or non-HD compatible) sets will simply not be manufactured anymore, at least not in sizes bigger than 13". Of course at that time I'm sure there will inventory blowout sales as they are discontinued, at which you might be able to pick up an old tube for very cheap.
In the same vein you might just want to check out some manufacture's seasonal patterns. Right as they are introducing the next set of models (with basically identical performance) see if your local store is dumping last year's for cheap.
I think you can get a decent 27" set with good comb filtering and component inputs, etc. for about $300 US. You can get lower but with less pq and connectivity. I think the bottom of the barrel is low $200s new.
I still believe that if you do not have a need for an HD ready set (esp if this is not for the primary room), then this is the more economical approach, since the HD set you would buy today can be had for less down the road when you can take advantage of all its features. Again, this assumes you cannot benefit from an HD ready set now any more than a standard def set. One negative to the now + later purchases is cost to the environment.