Keep your eyes open and you can find a Deere 1010 or early 350 crawler loader for $3000-$3500. They go cheaper then dozers. I just looked at a nice running Deere 350B crawler-loader last week that sold for $3200.
I've had a 1960, Deere 1010 crawler loader for years and its been a great machine.
One thing to consider though. A machine like a Deere with a hydraulic reverser - can be extremely expensive to fix if that reverser fails. Deere has also discontinued many parts for all the 350 series.
If you don't need the convenience of a good reverser - you might look for simpler crawler-loader with all gear-drive. Like an Allis Chalmers HD5? Oliver OC4? Great simple machines BUT the ACs have hand clutches.