Is the air in your home dry?
If there is dust, pollen or seed and pellet debris in the air, that could be contributing to the sneezing.
Using a warm mist humidifier in the room where your bird is housed would be very beneficial.
Additionally, you can put your budgie’s cage in the bathroom when you run hot water through the shower so the cage is in the hot steamy air -- that will help open the airways.
Another option is to tent the cage with a sheet and place a pot or kettle of boiling water under the sheet where your budgie is unable to touch it and allow the steam to accumulate that way. If you have pure eucalyptus oil, you can put one tiny drop into the water as that will also help to clear the airways so the budgie is better able to breathe.
Using a warm mist humidifier in the room with your budgies is a great way to help ease breathing problems.