There seems to be a huge difference in the amount people are spending on supporting peripherals for the Raspberry Pi. I just bought a set of twenty for my classroom (breakdown below) and ended up spending GBP855 in total - around GBP43 each. TBH I could have trimmed this down further, as the USB Hubs and multiple sets of HDMI-DVI adaptors are to make it easier for pupils to switch between the Windows PC on their desk and the Raspberry Pi; they only have to swap two cables instead of three, and HDMI connectors are a lot more user friendly than DVI for frequent connections/disconnections.
Had it been available the model A would have been ideal for our usage - the Raspberry Pi's will not be connected to our network for security reasons, and the extra RAM and additional USB port are of no great benefit for our use case (teaching pupils about alternatives to the Windows OS they have been using since primary school, teaching programming in a sand-box that won't endanger the rest of the network).
Breakdown for those who care:
20 x Raspberry Pi @ GBP23.98 each
20 x Cases @ GBP4.20 each
20 x Micro USB PSUs @ GBP4.90 each
20 x HDMI Cable @ GBP0.80 each
20 x HDMI - DVI Adaptor @GBP 2.24 each
20 x HDMI - DVI Cable @GBP 2.71 each
20 x 4 Port USB Hun @ GBP1.32 each
20 x 4GB Sandisk SD Cards @GBP 2.60 each