I paid $239, plus $60 shipping, for my 36V 10Ah LiFePO4, including a BMS and charger, which equates to pretty close to £150. Others on here are using the same packs, as are a lot of people on the Endless Sphere, and they do seem to be pretty good. I was lucky in that the package didn't get charged by customs, but if it had I guess I'd have had to pay perhaps another £35 or so in VAT and handling fees, still much less than half the price of those one's you linked to and with much greater capacity.
This thread:
TongXin (a.k.a. Nano) motor project ) has some pictures of my bike project and the battery, as well as the specs.
The seller of these LiFePO4 packs is Li Ping, in China. You can buy them relatively safely via Ebay (his shop is here:
eBay Store - PingBattery: 36V LiFePO4 Batteries, 48V 24V Battery, Electric Bike Scooter ). If you don't want to bid via Ebay, then if you email Li Ping he will make you a pack up and send you a PayPal invoice. He warned me a few days ago that the lead time for a new pack to order was around 10 to 15 days, as he has been selling a lot of packs lately.
Jeremy