I have an M20F with a fully loaded panel i bought recently for about 140k. GFC 500, dual G5s, GNX 375, JPI 900, Aera 660, lot time engine, and pretty much all the speed mods you can get as well. For the most part the only other thing I would want to upgrade is the interior, which is in decent shape but could use some work.
I think it would be hard to spend more than that on an F lol. I'm happy with my purchase, but can't say if I'm the most knowledgeable buyer in the world. I think there's a lot of value in buying something with the panel already done. Probably cheaper to buy into a nice panel vs put one in on older planes like this. That being said i doubt many people would go higher than that on an older Mooney.