Got some more specific numbers. Rachel, who was showing me around, brought up the fact that they could hook up xboxes and playstations to the projector before I even did. Closing time is midnight; evening pricing, which is a flat rate $1800, starts at 5. 31 March /is/ available. For 100 people, they'll need 4-5 staff on hand, which includes 1 manager ($145 <= 5h) and 4 staffers ($125 <= 5h), so if I ran things 5-12, 7 hours (including an hour of setup and party starting at 6), we're looking at $850 for staffing. Booze can be done more or less how I want: drink tickets, prepaid, cash bar, whatever. I'd most likely pre-pay a specific amount and after that's spent it reverts to cash bar. Drinks run as much as $8.50 for specialty cocktails, so basically bar prices. They /will/ do Dishwashers for me.
So, we're looking at $2650 for the facility plus staffing. Say, $1k for booze (even at $8.50 for every drink that's more than one drink per person), and a quick review of metropolitan market's catering menu tells me I can feed you moochers for between $5 and $15 per person, depending how much I decide I like you. So, I can probably make this happen for about $5500 or less. Which puts it pretty much where I wanted it to be.
So. I've just gotten off the phone, and booked the redmond facility for 31 March. She's going to send me the contract by email.
edit: Went ahead and spec'd $1500 for drinks, which will include non-alcoholic stuff too.