Insignia is the bestbuy house brand of TVs. It's a rebadged no-name TV.
As far as the cheapest TV you can get from any major manufacturer, probably philips, follow by Samsung.
http://www.outlet.philips.com/b2c_redes...BB9A6F008D00000000828BD472&shop=OUTLET
The philips outlet site has some hdtvs that are decent quality. Generally Philips are considered at the bottom of the barrel of the major manufacturers, but that's still better than a no name brand.
The televisions at the philips outlet are refurbished though, but the 30" for $344.99 (30PW8420/37B) is not a bad deal if you don't mind the lack of an HD over-the-air tuner. The 30PW9110D/37B ($435.99) is the same tv, but in black and with the tuner. The slightly more expensive 30PW9100D/37B is the same as the 9110D, but in silver. It may also have higher build quality, since the black 9110Ds were specially made for walmart and sold at a lower price originally by about $50.
I have the 9110D that I bought new from Walmart over the summer. Looks very nice, far better than any LCD TV even 3x the price that I've seen. Playing gamecube and xbox on it in progressive scan looks as good as a computer monitor. SD content quality seems fine, as does DVD playback, and HD OTA sources look fantastic. It may not compare to a Sony 960, but in general even a low end CRT HDTV looks better than LCDs at anywhere near the cost. (perhaps at any cost when viewing non-native res material)
I'd be wary of the Insignia brand though, besides not being a major brand at all, the picture quality is notably worse than Samsung or Philips when I've looked at the display models. The normal Samsung CRTs I saw at my local best buy were about $100 to $200 more than the same size philips, looked a bit better, and had less features, and the slimfits had a similar price over the Philips but looked worse.
In all though, CRTs are a dieing breed. On the market right now, the only real high quality CRTs left are the Sonys and even those aren't on par with their hey day, Samsungs mostly only have Slimfits out still, Philips are decent low end sets, and anything not brand name is crap that only exists to sell at low pries to people who care nothing about picture quality. Oh sure, Panasonics and Toshibas are still on the market, but they fall in a price range between Samsung and Sony, and there's quite a gap. (in your price range, only philips and off brands exist, and maybe the occasional samsung)
Oh, and no CRT HDTV supports 720P. All are 1080i, however they can scale 720p to 1080i fairly well, CRTs have less of a problem with non-native resolution sources than other displays do. Well, all CRTs attempt 1080i, technically not a single one can display the full resolution. The closest was the Sony 960, at something like 1400x800. Most others fall around 1000x600. Still, for CRTs the low resolution isn't as much of a problem as it is for LCDs since they don't have discrete pixels, and their color accuracy is so much better.