Resources
In our case, the best resource to explore Guyana was the Bradt Travel Guide about Guyana, by Kirk Smock. It was extremely useful. It was a bit outdated, but we know that very soon he is publishing an updated version. It is highly recommended to get one before starting organizing your trip.
Tips
The main thing that we can recommend you is to start organizing your trip as early as possible. Sometimes it takes time to get a response to your emails. Many places in Guyana don't have Internet access, so the people you are trying to contact might only check their email once in a while. Be patient. The phone also works most of the times. Use Skype or other Internet service to save some money for the trip itself. Other places in Guyana don't even have phone access, so I highly recommend planning your trip carefully before you start it. Bagpacking without a well defined plan can turn to be very difficult. Don't desperate, your effort will be rewarded!
Budget
It is true that Guyana is an expensive country if compared with any other South American country. However, it is totally worth it to visit this hidden gem. Most of the times you will be the only visitor in a town. It is an authentic experience that you will remember the rest of your life. We read in some forums people saying that you need more than 250 US per day. In our case, we spent below 100 US per person and day, including all sorts of transportation, accommodation and even a trip to Kaieteur. In any case, every single price is specified in the different sections of the website.
How to get there
In our case, one of us was already living in Georgetown. One of us came from the US. The easiest way is to fly from New York (JFK) with Delta Airlines or Caribbean Airlines. The other of us came from Spain. We found that the easiest and most economical way was to come to Georgetown through New York. However, while traveling in Guyana, we found another interesting routes. From Frankfurt you can travel to Tobago, then to Trinidad and then to Georgetown. From Amsterdam, you can fly to Surinam and then to Georgetown. The price can really vary.
The day that one of us was arriving a plane crashed in Georgetown. Fortunately, there were no casualties. Don't worry, it has been the only accident in the history of the airport. It was not her flight, but she was only two hours from Georgetown when it happened. The airport was then closed. Delta, for some strange reason, decided to send her flight back to New York city, instead of landing somewhere nearby, like Trinidad or Surinam. She was trapped 2 days in the airport. Delta's treatment was awful. She didn't even get a hotel room. Even the accident was not their fault, how they treated passengers was really terrible. Originally, Delta told her that she would need to wait 9 days in New York. Finally, she arrived 2 days late. It affected our trip, but we were able to reorganize it. They never compensated her in any possible way.
The day that one of us was arriving a plane crashed in Georgetown. Fortunately, there were no casualties. Don't worry, it has been the only accident in the history of the airport. It was not her flight, but she was only two hours from Georgetown when it happened. The airport was then closed. Delta, for some strange reason, decided to send her flight back to New York city, instead of landing somewhere nearby, like Trinidad or Surinam. She was trapped 2 days in the airport. Delta's treatment was awful. She didn't even get a hotel room. Even the accident was not their fault, how they treated passengers was really terrible. Originally, Delta told her that she would need to wait 9 days in New York. Finally, she arrived 2 days late. It affected our trip, but we were able to reorganize it. They never compensated her in any possible way.