Wot Jed said.

The single mike idea is old technology; you know, the way they used to do it in the "goodle days". There's a lot of groups going back to it (Steve Earle with the Del McCrory group comes to mind), but it requires players who can balance their own needs with the group's needs (& put the group first). The choreography involved in bringing each solo to the forefront becomes part of the show.

The other thing to consider is that looking at a sound person as an add-on luxury just don't work. The sound tech is a PART of the group; particularly if you find one compatible with your own vision. He/she is part of your sound, as much as the fiddle player or mandolinist, and should be looked at and treated as such. Here endeth this particular sermon :-)