In MIDI 1.0, you only need to purchase a Manufacturer ID assignment if you want to specify a new kind of System Exclusive message (or a new kind of Sequencer-Specific Meta Event).
If you only need to send an existing format of System Exclusive message (or store an existing format of Sequencer-Specific Meta Event), then you would just use the Manufacturer ID of the existing format. As long as you do not extend the format of the message in a new way, you are allowed to use other manufacturers' messages.
If you are only developing messages for your own private use, you can use the non-commercial Manufacturer ID (hex 7D) which is "reserved for non-commercial use (e.g. schools, research, etc.) and is not to be used on any product released to the public." But if you want to publicly describe your new message, I think you would need to purchase a Manufacturer ID assignment to prevent conflicts.
(In the MIDI 1.0 Detailed Specification
, see "System Exclusive Messages" starting on PDF page 39 / printed page 34.)
(In the Standard MIDI Files Specification
, see "Sequencer-Specific Meta-Event" on PDF page 12 / printed page 10.)
(To see a list of Manufacturer IDs, on this website's footer, go to the "About the MIDI Association" page, scroll down to "Manufacturer System Exclusive IDs", the click the link "The MIDI Association publishes a list of every assigned System Exclusive ID number.
After a quick look over the MIDI 2.0 specs, it looks like to start a MIDI 2.0 connection, an Initiator has to send a Discovery message and the Responder has to send a Reply to Discovery Message. Both of these messages have fields for Manufacturer ID (as well as Device Family, Device Family Model Number, and Software Revision Level). (In the MIDI-CI Specification
, see "5.5 Discovery Message" starting on PDF page 22 / printed page 17 and "5.6 Reply to Discovery Message" starting on PDF page 25 / printed page 20.)
However, each device generates a random MUID on startup (or regenerates a new random MUID in the rare case it detects a conflict). The Discovery and Reply to Discovery messages include these MUIDs, then it appears the rest of MIDI 2.0 messages use these MUIDs to identify the Source MUID and Destination MUID of each message.
So if you are developing software that just wants to query MIDI 2.0 devices, I think you would only need a Manufacturer ID for the initial Discovery message. I can imagine developers that want to query MIDI 2.0 devices but don't have resources to purchase a Manufacturer ID might decide to violate the spec slightly by using some dummy Manufacturer ID in the Discovery message. (Say, perhaps, a Manufacturer ID of hex 7D [Non-Commercial] and zero values for the Device Family, Device Family Model Number, and Software Revision Level.)
This could become messy however. If you ever have a need to define some response or value or profile that is specific to your software, you could be tempted to start defining your own values, but if other developers used the same dummy Manufacturer ID and developed conflicting definitions it would be an incompatible mess. To prevent that, the MIDI Manufacturers Association would probably want you to purchase a Manufacturer ID assignment, and would probably not endorse using a dummy Manufacturer ID.
But perhaps the MIDI Manufacturers Association might consider defining a special Manufacturer ID in the Discovery message for developers that only want to query and control other MIDI 2.0 devices and not define any values or profiles for their own software. (Say, perhaps, allow use of the Manufacturer ID of hex 7E [Universal Non Real-Time] in the Discovery message to represent this "query and control only" usage.) However, I don't yet understand all the details of MIDI 2.0 to know if this is a workable idea though.
Purpose of fees
On this website's footer, go to About the MIDI Association
to read about the MIDI Manufacturers Association's purpose and the cost and benefits of corporate memberships ($600 to $20,000 per year, based on company sales revenue) or non-membership Manufacturer ID assignment fees ($240 per year).
Because the MIDI Manufacturers Association is a nonprofit organization, you can see their IRS returns
to get an idea of how they use their money. (Note recent data is missing -- the IRS says
"Expect delays in data updates for the Tax-Exempt Organization Search tool. We are still processing 990 series received April 2020 and later.")