Yeah petstores can be hit or miss, depending on the people working there.
If the snake rack I ordered ages ago would have shown up I could probably sell you a relatively good priced deal on a 20 gallon long tank plus screen lid plus UTH, would only need a thermostat to regulate the heat. I don't know when my rack will arrive though, so all my 20 gallon longs are still occupied for now.
As far as heat I'd recommend a UTH and thermostat. That is all I use here, even in winter (though I usually have the house at 68 minimum). Heat rocks are notorious for causing burns, especially if unregulated. I just put a UTH under one side of the tank, covering about 1/3 of the area of the tank. After they eat they will usually lie on top of the heat to digest. UTH can also get too hot if unregulated though, so a thermostat or rheostat of some sort is a must. I use this one:
http://www.reptilebasics.com/ranco-etc-111000-pre-wired There are better and worse variations (and more expensive and cheaper), but this one suits my needs.
Just for a quick idea: I once ran a UTH unregulated without a thermostat just to see how hot it would get (no snake in the enclosure at the time I did the test). The UTH reached over 110 degrees before I finally shut it off....way way way too hot for a cornsnake, and could easily kill the snake at that temperature, which is why a thermostat is so important.
I don't know if anyone has experience with this one:
http://www.bigappleherp.com/BAH-1000-Thermostat?sc=2&category=15 But looks like it might work. I prefer digital readouts myself though, rather than an analog control like this one. Just make sure you also have a digital probe thermometer to monitor the temps, can pick a probe thermometer up at home depot or wal mart for around 10 bucks give or take (the type of thermometer you keep in your house but also has a probe on a wire that you can send out your window, so you have "inside" and "outside" temps. Put the probe part in the tank above the UTH and read the "out" temps.) (I'd use a thermometer with any thermostat just to keep an extra monitor on it, never know if a thermostat will crap out on you and a thermometer is another way to keep an eye on the temps).
Something like this thermometer:
http://www.walmart.com/ip/Acu-Rite-Indoor-Outdoor-Thermometer/896347
Herpstat proportional thermometers are probably one of the most recommended thermostats:
http://www.spyderrobotics.com/products/herpstat.html but they are going to cost a bit more.
The cheapest alternative is to get a lamp dimmer from home depot
http://www.homedepot.com/webapp/wcs...63-2&AID=10368321&cj=true&srccode=cii_5784816 However, this must be manually controlled (output adjusted up and down by hand), and the temperatures of the UTH must be monitored very closely by your own eyes with a thermometer for manual adjusting as the temperatures will change if your house temperatures change. It's just easier to get a good thermostat.
In summary, for heating I'd recommend:
1. UTH (under tank heater) (can find these at petco/petsmart/etc)
2. Thermostat (more preferable than a lamp dimmer type rheostat) (probably order online)
3. Digital probe thermometer such as
http://www.walmart.com/ip/Acu-Rite-Indoor-Outdoor-Thermometer/896347
Also, I don't know what colors you are looking for or what you want to spend, but I have a couple 2011 hatch butter stripes still available, and wouldn't need to pay for shipping. I'm also expecting some hypo, lavender, motley combinations in June (provided egg laying and hatching all goes well), but don't know if you'd want to wait that long. The W.I.R.E show will be in Madison on April 22 I think, but I've never been to that show and don't know how represented cornsnakes are. Or you can search the classifieds on this site and find tons of snakes for sale.