The final deal is apparently £13 million plus Ngog. If you ask me that's good business for Liverpool.
For that price, they shift some dead wood with the potential of a future success. Even if Henderson does completely flop - his name alone will probably be able to sell for about £5 million meaning a loss of £8 million, which isn't terrible for a club of Liverpool's size. Personally I think he'll do well.
And Barca probably can afford Cesc, but how much will they pay? Today they openly came out in saying they had £40 million to spend on players plus any money from other sales. I imagine Fabregas is valued at around £40 million, which may just be too much for Barca.