Suppressors transfer from manufacturers to dealers on a form 3. Only dealers that have a SOT can transfer suppressors that are on a form 3. You have an option to do paper forms, old school or e-file . E-file has been really fast. Paper forms have been taking 9 months.
Privately owned suppressors that are on a form 4 may be sold to a person in the same state on another form 4. If the person is out of state, it has to go to a form 3, at a SOT, then transferred to a dealer in the new state, on the form 3. The new dealer will transfer it on a form 4 to the new owner. Each time a nfa item transfers involving a form 4, it costs 200. So form 4 in state costs 200. One out of state is 400, plus any dealer fees.
Privately owned form 4 to form 4, currently can only be done on paper form 4s. So plan on waiting 9 months.