Xbee pro s2c 2.4 ghz 10dbi Antenna and its effect
Does antennas draw more power if their gain is higher? No, the power is set by the RF module, the antenna gets a certain amount of RF power and that's it.

That "gain" rating is deceptive as it is not really gain in all directions. Read this. A higher gain antenna will just direct the power (and be more sensitive) in certain directions. It will transmit less power and be less sensitive in other directions.

So you can use "high gain" antennas to increase the range but you will have to make them "see" each other. And if one of the devices is not in a fixed position, overall range might end up being less than what you had.