I searched around a bit and the most basic quotes for public liability should start from £89 or so, according to this insurance article. But of course the price depends on how much experience you've got and what type of work you're doing.
My Lenovo Ideapad has served me well for 5 years and counting.. I'd recommend looking up cheaper online stores and ordering from there, not from a big store which would charge you for their overheads, advertising etc as well.