How about some paper cups and some bits of string?
Seriously, without the budget to buy radios, or hire a comms system and with zero time available, I'm not really sure what you hope to achieve. If Skype isn't an option, how about a Google Hangout or something similar? Why can't you use a laptop, you don't make that very clear.
Depending on how low-tech you want to go, there's always the trusted torch to flash at the operators. I'm really not sure what other options you have!