Getting to San Ignacio, Belize
The basic layout of Belize from the northern border to the western border is more or less this: border, Corozal, Orange Walk, Burrell Boom, Belize City, Belmopan, San Ignacio, Benque, western border. You can skip Belize City if you are driving and head straight to Belmopan. Driving from San Ignacio, it's 30min to to Belmopan, an hour to the City, 2hrs to Orange Walk, 2.5hrs to Corozal and 3hrs to the border. If you are taking the bus add 30-60min to each time depending on what bus you take. So Belmopan is an hour Belize City is 2hrs and so on. The fastest way to get around is in your own car or a rental, next up is taking a shuttle which is more expensive and the cheapest/slowest is the bus. They will all get you where you are going; it's just a matter of how fast you want to go.
To be honest it usually works out quite a bit cheaper to rent a car if you are going to be around for a few days. You'll be able to get to a lot of neat places that you would normally have to get a fairly expensive tour to see - Mountain Pine Ridge and Caracol are two great examples. If you don't want to go the car rout and you don't like tours, it's still totally possible to get around by bus so don't worry.