I would like the ability to monitor the temperature in all 6 racks but I don’t want to break the bank. Can you help?

Certainly. Any of the products in the Rack Environment Monitor section would satisfy your requirements. All rack mounted environment monitors support additional probes. So you can place the environment monitor into one of your racks and then locate external temperature probes into each of the other 5 racks. Products to look at include the AKCP SensorProbe8. Alternatively, if you'd prefer reduce the amount of wiring you need to do, you could go for a product like the AVTECH TemPageR and place one unit in each rack.