Range Extending - Cables And Speed Limits?

I'm an electrical engineer by trade, and fairly inept at networking. That being said, I am looking to extend the maximum range of my networking equipment. I have a job which requires around 500' between switches, and am trying to find a clever way to bridge the gap. The span is direct-burial cat5e, and has very low bandwidth requirements. I know you can buy off-the-shelf range extenders, but they are expensive, so I thought maybe I could avoid it.

1. It my understanding that the lower speed protocols (10 Mbps rather that 100, 1000) have a longer maximum operating length, because they utilize a lower frequency and consequently see a lower impedance. If so, are there network switches that I can force to use the lower baseband frequencies?

2. Should I bother trying to find a cable with the lowest characteristic impedance (or will they all be similar)? Cat 5e is pretty good, yes?

3. Should I do half or full-duplex; is this something I can control as well?

4. What network switches are cheap and allow this type of configurability?

5. If I attach other switches to the ends of this 500' ethernet bridge with auto-negotiating feature, will there be any conflicts or they will all get along?