First, find a hardware store, a place that sells viewcams, mappers, etc. Split off one of your droids and talk to the shopkeeper, making sure he is the the "Buying Stuff" part of a conversation. Switch back to your cluster of other droids and fire one shot at the one talking to the shopkeeper. Switch back to the speaker and end the conversation by clicking on the mouth, and then say "Thanks, bye now!" Regroup your droids and talk to the keeper again. All the expensive city mappers, viewcams, radar units, and anything else you plug into the droids, will now be reduced to 10% of their original price!

This doesn't work all the time, so try a few different things, such as instantly ending conversations by running away, or just using one droid to talk and then leave without buying anything.