Garry87
Yes there is a huge difference.
When coming to Barbados take USD and GBP from the UK. Don't purchase BBD in the UK as you can receive a much better rate in Barbados. If you purchase BBD in the UK the rate won't be nearly as generous and is currently around £1 to $3.07. In Barbados, you'll get about $3.28 currently for £1. If you take UK Traveller's Cheques, you'll get an even better rate. Currently it's $3.33 to £1. You can do the exchange at any of the several commercial banks on the island including CIBC First Caribbean International Bank, Republic Bank (Barbados) Ltd, First Citizen's Bank (Barbados) Ltd, Scotiabank or the RBC Royal Bank. They all have the same rates as set out by the Central Bank of Barbados.
I would recommend you get your USD from M&S Travel Money which is commission free with very competitive rates. Currently you get about $1.62 USD for £1. USD can be spent on the street in Barbados at $2 for $1 USD. However, in some stores/restaurants, you will receive anything between $1.95 and $1.98. Anywhere around $200 to $250 USD in small bills ($5s, $10s and $20s) should suffice to get you started and for tipping. Whatever USD you don't spend, you can either hold on to it for a future trip as it's a globally accepted currency, or you can sell it back to M&S.
Also take your credit/ Visa Debit cards.
Hope this helps
Regards