What about the Airport that looks like a gumdrop? I see those on ebay for about $50.

The main users of wifi are in our office. A single Airport Extreme should be able to cover that area, and the guest wifi feature might actually be useful (if it's available when in AP mode).

Suppose I got a (new-style) Airport Extreme for the office, and then filled in the gaps in the warehouse with gumdrop Airports? They're only 802.11g, but that's perfectly fine out there. The only concern is that WPA2 might not be supported.