This is so off topic of blue hole flights....but a beer is $4-$6 BZ at most places. You can buy a case of 24 at the distributor for $50BZ.
Soft drinks cost about $3BZ in a store...but i'm not sure, we don't drink it.
Meals vary widely in cost. At small stands you can get a good meal for around $10-$12 BZ. Meals at some restaurants can run $50BZ plus drink and tip. Breakfast will run $10 BZ at a place like Glendas, even less at Marins. Similarly you can get a chicken burrito bigger than you can eat at the split for around $10BZ.
We recently spent a month on island and as I recall spent around $1,000 US for expenses (not including housing). We didn't eat out a lot since we had a cooktop and refrigerator. This included things like water taxi.
Hope this helps. Keep in mind you can spend as little or as much as you like, Belizians are descendants of pirates LOL.