I just looked on Farnell and the cheapest solenoids that I could find in stock have a weird housing (and they're £6.38 each which is already more than Amazon), the cheapest sensible ones that are in stock are £12 each, which is way more expensive than Amazon, plus you have to pay VAT and postage on top, plus you have to faff around with their enterprisey order form, compared to one or two clicks on Amazon.