Hi Alan
It's always difficult to say as we all spend differently on holiday.
Personally I would allow about £20-£30 per day. Most of your meals are included so you will need to buy seven lunches, plus drinks, snacks, souvenirs, tips and any other everyday expenses.
Bear in mind also that although Cuba is a poor country it isn't cheap. The government has set the exchange rate for the Cuban Convertible Peso (the currency for visitors) at an artificially high level, so you will be paying the same sort of prices you would in the UK.
You are right to take cash as ATMs are few and far between in Cuba.
Have a great trip - Cuba is a fascinating country and truly unique.
Kind regards,
Olly, your editor