Although with hindsight I wish I'd bought something with more updated avionics.
To be fair, that's not really an issue any more, because if by 'avionics' you mean GPS, moving maps, etc, just get yourself an iPaq, Bluetooth GPS and Pocket FMS, and a copy of NavStar on a laptop (optional), and presto, all the avionics you ever needed!
(Although if by 'avionics' you mean autopilot, HSI (I'd guess a Mooney has one anyway) and radios, then that'll be a bit more challenging.)
Out of curiousity, what model Mooney is it? What are the maintanence (can never spell that) costs like? I've heard they range from very high to very low, but it'd nice to have more then a rumour to go by!
Confab