Cheap IFR GPS (M3 approach ?) advice

Hi all,

I am toying with the idea of installing a "cheap" IFR GPS in my '76
Cardinal. Being admittedly a bottom-feeder in this area, my choices
are basically limited to a used KLN89B, or the Northstar M3 Approach,
something like a $1500 setup total.

I don't think an avionics shop would touch anything like that for
under $1000 in labor (can't really blame them, its probably *harder*
to install than a latest generation unit), so I would be doing the
work myself with an IA's assistance & signoff (and some begging at the
FSDO). The M3 seems particularly attractive in this regard, because it
is so simple to install when you use the MD40-64 indicator with
built-in lights (no OBS, switching, etc). I also much prefer its
interface to the older generation King units. My only concern is the
near-term (say 3-5 years) availability of database updates for the M3,
has anyone heard any rumblings about this ? Jepp seems to offer the
Skybound II service for the Northstar right along the Garmins and
Kings, but not sure what their policies have historically been about
discontinuing updates.

I should mention my primary motivation for wanting the GPS is
flying direct without having to beg for fake vectors, and filing lower
on airways with high MEAs that have considerably lower MOCAs. The
approach capability is secondary, but since it just involves one extra
annunciator light (at least on the Northstar), I'd try to get it
certified. I do understand these first generation A1 units will be
throwaway when the precision guidance becomes reality, that's OK, I am
just looking for something I could put in cheap and use for the next
3-5 years.

Thanks for any comments, particularly from current M3 owners or
someone who has rolled their own (any brand). I think I have a pretty
good understanding about all the things required to have the rig
IFR-blessed (encoder interface, CDI, annunciators, COM interference
testing, AFM supplement, etc.), so I am looking for war stories about
the certification process itself when avionics shop wasn't involved.
The IA is willing as long as the stuff has some basic pedigree
paperwork (tagged, 337 sample, some continued airworthiness writeup).

Thanks!

Martin