(2-part post):
It's difficult to do the sums accurately because the HMRC website gives the rate of duty as 4.9% to 14%.
http://customs.hmrc.gov.uk/channelsPortalWebAp p/channelsPortalWebApp.portal?_nfpb=true&_page Label=pageTravel_ShowContent&id=HMCE_PROD_0099 89&propertyType=document
Without knowing the exact specifications of the cameras, it's hard to be sure what rate of duty will be charged. However, I understand that the higher rates only apply to cameras which can accept an external video input (allowing them to be used as video recorders). I'm going to assume that the 4.9% rate applies.
Further, since you've given the value as US$200 to US$400, I'll assume that the total value of your consignment is roughly 10 x US$300 = US$3000.
So, you've got 4.9% of US$3000 to pay in duty, which is roughly US$150.
Then you've got VAT to be added on. This is 17.5% of (value of goods + duty + carriage). I'll ignore the VAT on the carriage, but 17.5% of US$3150 is about US$550.
So that brings the total bill to US$150 + US$550 = US$700. There's also a customs examination fee to be paid but that's fairly small.