The following table includes the cheapest prices for Raspberry Pi accessories, including the price of the Raspberry Pi Zero:
|£4.00||Raspberry Pi Zero|
|£2.59||8GB Kingston MICRO SDHC MEMORY CARD|
|£2.84||New 4 Ports USB Multi Adapter Travel Wall AC Power Charger|
|£2.09||5x Micro USB to USB Retractable Data Sync Charger Cable|
|£2.81||USB 2.0 to LAN/RJ45 Gigabit Ethernet Network Adapter & 3 Port Hub 10/100Mbps|
|£1.88||USB 2.0 Virtual 7.1 Channel Audio Sound Card Adapter|
+ + = £8.69
Raspberry Pi Zero + micro USB with 3 port USB hub LAN adapter + USB sound card = £8.69
Raspberry Pi £29.99 - Raspberry Pi Zero (with model B features) £9.90 = £21.22
That means the Raspberry Zero including 3 x USB ports with USB ethernet adapter and USB sound card is over £21 cheaper than the original Raspberry Pi model B.
Note: I have not included the price for the header pins and the time taken to solder the the header pins into the GPIO holes on the board. The price I found on eBay was £1.68 for 2 pairs 40 Pin Header Female + Male Pins Sockets SIL 2.54mm Arduino Raspberry Pi.
Use a Raspberry Pi Zero instead of a Raspberry Pi B unless you have a specific reason why you would want everything already assembled (i.e. convenience).