As I figure it, if my arithmetic is correct, comparing costs for roundtrip tickets plus cab fares if going to municipal it's roughly a wash with one person and you save money with two or more by flying roundtrip via the municipal airstrip versus international.
With three or four persons you get some fairly serious savings.
Even with just three persons, you save over US$100 total , enough to buy about 30 or 40 Belikins.
Of course it is more of a hassle and coming back it's frustrating (and irrational) to land at international, then fly on to municipal, and then have to taxi back to international.
Figures shown are for current roundtrip flights on Tropic (Maya Island may be slightly different) plus taxi fare to and from municipal (taxi fare is for the cab, not per person). Figures are in US dollars. Air fares don't include any cash discounts or tips for cab drivers (I don't tip cab drivers in Belize unless they handle a lot of luggage.)
1 person: $120
2 persons: $240
3 persons: $360
4 persons: $480
1 person: $67 +25 + $25 = $117
2 persons: $134 + $25 + $25 = $184
3 persons: $201 + $25 + $25 = $251
4 persons: $268 + $25 + $25 = $318