In defence of San Pedro you can do quite well on the cheap here, there are plenty of places to stay and meals need cost no more than $5 to $10BZ per person, often with enough to eat for two. Big Daddy's is open most nights until 6am and unlike Cancun you don't have to pay a huge entry fee to get into the clubs ($50US per person in one case last year). Renting a windsurfer is only $35US per day if you rent by the week.
Plenty of backpackers come to the island and have a great time. They wouldn't keep coming if they weren't having a good time.
Listen to the people that love this place there are far more of them than those who seem to have a bone to pick with Belize.
BTW, let's get the facts straight - it's $35BZ round trip to Caye Caulker.