They've said the ME franchise will see no type of expansion. Expansions are old school, not new school.
Maybe if they planned it in an episodic nature: a mission meeting up with the Virmire survivor, fighting alongside them, fulfilling some pro-Alliance mission objective, and ending with the Virmire survivor leaving to report in and what not. And then the next piece of DLC picks up, no Virmire survivor, but Anderson and Hackett, let's say, offering to patch things up with Shepard, or something.
That might be one way to do it, while keeping individual DLC costs down. Really, $10 is as high as DLC should go, and even then only rarely.