Charlie,
As you know "finance" is a top PPC keyword so would have thought Financecenter.co.uk would be worth more than £100, especially if it has traffic. However, "center" is obviously not the best for the UK market being the American spelling.
Has it been earning on Sedo?
MarineChart.co.uk is a more specific genre and has a much smaller market scope so would let it go for £100 unless its traffic is significant.
Admin