The ending just needs finalising, not necessarily any gameplay, ie shooting things.
Example: If we use indoctrination as the basis of the ending, shep will wake on london. He comes to, around the point he comes to before going past maurauder shields. Remember what beating husk saren did to sovereign? Same thing to Harbinger. As Shep gets to his feet, the parts of hammer that weren't in the charge have finally made it, and blow Harby a new a-hole. How it goes from there can differ. You could say that the crucible isn't a weapon, but a means by which to defeat indoctrination, thus rendering a reapers power over people null and void, and destroying harby creates a reaction amongst other reaps which overloads them, seeming as he could be in direct control over all of them. You and hammer could go in thru the conduit and unleash the crucibles power, although obviously events would play out differently. Or shep could be too injured and hammer with a living anderson could go in and finish the job (assuming of course dave death was indoctrination ploy). Obviously, if you succumb to indoctrination, then the end plays out different. Remember these ideas need no gameplay, its just a long cutscene with dialogue choices.
As for if its not indoc, then check out my idea for an ending here
http://social.biowar...8105/2#10239474
As for paying the vas, i'd imagine someone like freddie would cost more than seth. I'd imagine someone like seth, or jennifer or ana hillis or any of the veteran ME voice actors would do it regardless of money, they love it too much. I know i, as an aspiring thespian, would love it and would probably do it for free