If you want to find the best deals on vacant land in Colorado you need to deal with the people who the investors buy from. There are endless companies that sell vacant land, some on Ebay, others from their own web-sites but you need to weed out the garbage and find the real deal. Your best bet is to find a realestate company in the area that specializes in land and has an actual office you can walk into. You should find a land agent who has listed properties from sellers and who actually will be eager to show you the property. Dealing with a good realestate agent will give you a certain amount of confidence thereby letting you concentrate on getting a good deal vs. worrying about getting scammed by a private seller.
You will find that the preferable real estate companies are usually the mom and pop operations that have just a few agents. When you Google for companies, consider that many of the very best deals will not be found through Google. Google is going to display mostly generic fly by night web-sites that are directed at generating clickthroughs more than anything. Try the old fashioned way, call some local business owners (really any businessperson in any profession will usually give you their honest opinion) and see who they recommend.
When you find the company and agent you wish to work with look for the cheapest property with the most amount of acreage. There is almost always a problem with the cheap land or it wouldn't be cheap. What you want to find is something with a problem you can remedy. A good example would be let's say 640 acres for $250 per acre without legal access. Now without legal access the county will not issue you a building permit. If you buy the property and can get legal access (I've seen it done many times before, it just takes some work) the property becomes much more valuable. Other examples might be title problems, water issues, railroad tracks, high voltage power lines and so on. Whatever the problem is, use it to your advantage. Some issues you just can't fix and that's understood so move on to the next property. When you find the right property make sure you can do what you want with the land before you buy it. Make sure you can build on it, get a well and put in a septic, subdivide.
To sum things up, don't rely on the internet to find you the best real estate company to work with. That perfect company probably is on the net but chances are they aren't easily found on Google and other search engines. Find an agent who specializes in vacant land in that particular area and it will greatly increase your knowledge base. Look for cheap land with a problem and research if you can fix the problem. If you can fix the problem you might be able to make a very healthy profit. The following link will take you to an ad for 320 acres that is listed by a company I consider to be a good example of what I've been talking about.