Dear Gillian and Graeme,
The unofficial exchange rate today is 3.3-3.4 BS to USD see Venezuela fx Bolivar-Dollar Swap Exchange Rate
which you can access easily to confirm ongoing rates. Subsequently as the official rate is 2.1 (IE through ATM) the choice (with the usual caveats) is yours. However USD, perhaps even Euros before Pounds.
The rate not so long ago here was 5+BS per USD and indeed you will find prices have consistently kept their high USD/ratios, even although the USD conversion has fallen some 40%. So although many thngs are considerable cheaper here in comparison to outside, no longer is it quite such a bargain.
USD in Trinidad is easy to obtain. There are a number of Atms which pay out USD. Specifically at Royal bank branches at Park Street and Ellerslie Court...(Beside Kentucky Fried chicken on North Circular Road maraval). There are others but these are the ones that I use/know when I visit my place in Trinidad.
If you PM me i shall give you my contact numbers and if I can help you re Trinidad or Venezuela
. then i shall be happy to do so.
I shall also give you the Personal Blog details of some friends of mine whom have spent a year travelling around latin America, using Public Transport and I am quite certain that all the bus details you need are easily obtained there.