The balloon payload is too small and light to have enough power to talk to Earth directly via radio. So, the payload will need to use a relay station. The relay station could be a secondary part of the mission, sent with the balloon. However, the orbiter would be much larger and heavier, and drive the cost of the mission beyond the Scout level. In addition, there are already multiple orbiters around Mars, which are designed to relay information between landers and Earth.
The first of these orbiters in terms of desirability is the Mars Reconnaissance Orbiter, launched in 2005 and which arrived at Mars in 2006. This large orbiter has a powerful telecom system, designed to act as a relay between Earth and Mars. Key to the balloon mission is the UHF radio, which uses the proximity 1 protocol to talk to rovers, landers, or other Mars probes. The UHF can handle 2Mb/sec or 4Mb/sec traffic.
The second choice for telecom relay is the older (2001) Mars Odyssey orbiter. The orbiter has less bandwidth in the UHF radio, around 256kb/sec.
By careful use of these two orbiters, image and science data can be transmitted to Earth reliably while not requiring a heavy transmitter on the balloon payload.