When I arrived at Belize in January, I decided not to pay $17.50 to get to town and had a pleasant half hour stroll to the highway. There I sipped a beer at a little store while waiting for a bus, which cost $1.25 US. Of course, I travel lightly, but it isn't that much of a walk at around two miles. I did the same coming back, but the bus ride was with another company and was even cheaper.
You don't have to spend outrageous sums to get into town.