
There are buses from Belize to P.G. The express bus takes something like 5 hours and the regular around 6 or 6 1/2. This is certainly the cheapest option.
Maya and Tropic have (or had?) flights to P.G., but (as of 9 Dec 2007) they were threatening to halt service because of the state of the airstrip. (Tropic flight is approx. US$100 from the international airport.)
You can also get a boat from Livingstone, Guatemala, on Tuesdays or Fridays in 45 minutes or from Porta Barrios, Guatemala, any day in about 1hr 15 minutes. If you are in Livingstone and want to travel on another day then you can always get a boat from Livingstone, any day, to Porta Barrios, this takes about half an hour. The boats will not run if the weather is too bad. These routes represent a southerly route from Guatemala which works round the lack of a southerly land route. You can use this route from Tikal by taking the bus to Rio Dulce, town, and then boat along the awe inspriring Rio Dulce, river which ends in Livingstone.
P.G. is small and walkable.
There is a Belize Bank with an ATM that accepts most foreign cards. The bank will only let you buy US$50 and charge a US$2.50 service fee. You can change your Belize Dollars for Guatemala Quetzales with moneychangers infront of the immigration office and at some hotels at a rate of Q3.5 for BLZ 1(a 10% loss).