I just received the invoice for the first annual on the 231 I bought last fall. As with most of the 14 airplanes I've owned, I did not do a pre-buy inspection. And, as with a number of airplanes I've owned, I did not see this airplane "in the flesh" until it was delivered to me.
The flat rate annual at my shop for a Mooney M20K is $2,380.00. The main IA I work with personally flies a Mooney Rocket so he knowns Mooneys and Mooneys of the 231 persuasion. First annuals are always eye opening, right ? And if you don't do a pre-buy, you're a fool and most here would tell you to add a zero to the invoice if not just expect to part it out once you do that first good inspection.
My annual was in and out of the shop in five business days and the final shop invoice was $2,796.64.