i vote for 50 slot for 3 months so $15/month.  I am sure we can get at least 9 people to pay $5 each, and the rest will sponge.  we could even have the officer, council pay for it as an obligation to serve the masses.  be about $3.75 each for 3 months, or $1.25/month so the whole guild can be on vent when doing even larger instances.