I think there are some exceptions like at MMSL where there is no GA ramp (so MMSD is much much cheaper in most cases, but horrible experience getting a multi-entry permit there). Best to call ahead or search for whether there is a GA ramp (rampa para aviacion general) at your intended destination and whether space is available (some airports like MMPR have very limited ramp parking), or be sure you fully understand FBO fees before flying in blindly.