AERCO: Instrumentation for Audio and Industry

What is the turnaround on the MP-2?

Approximately one month from the date of order.
Can the MP-2 have variable gain?

Yes, variable gain is an option with the MP-2.
If you make one with variable gain, is there any audible click when adjusting it as there is with the stepped gain unit?

Certainly not initially, but that's my complaint against tiny pots — they eventually go noisy. Even big pots tend to do that: it just depends how much wear and tear the shaft gets. Just means they have to be occasionally lubricated or replaced.
What is the price on the MP-2?

The price is $750.00 USD.
What is the run time on the MP-2 with three 9v batteries?

With no phantom load they'll run the preamp continuously for about 40 hours. With a heavy phantom load it runs for about 10 hours continuously.