If your only criteria are low rent, public transit, and job availability, you should probably post your question on the General US forum, cast as a sort of "Is there an area that meets these criteria?" CO would be doable, based on the first two criteria, at least (and depending on what part of the state you move to).
To get the bad news out of the way first: The job market here is getting grimmer by the week, though our unemployment rate (at 6.1%) is below the national average. Construction work, as brightdoglover pointed out, is also very weak here, just as it is in most places around the country. Even the Western Slope, which was booming as a result of oil and gas demand, has slowed with weakened demand, I've been told. And, finally, as everyone on this forum will tell you, it would not be a good idea in this economy to move here without a job lined up before hand.
For public transportation in CO cities, here's a link so you can see what's available.
APTA: Colorado Transit Links
I'm familiar only with RTD, which covers Denver and six other surrounding counties. You can do a search of the Denver forum for what people have to say about it. I use a few lines from time to time and the bus service seems just fine to me.
As for rents, you should probably check craigslist once you've narrowed down your list of towns (CO is a pretty big state compared to VA). I did a cursory check and Denver and the Springs, at least, have apts in your range. For Denver, you can also try the online listings in the Denver Post/Rocky Mountain News and Westword. Other town newspapers probably also have additional listings.
Hope this helps and good luck in your search!