Thank you all.

To the poster that mentioned the air compressor veturi type of vac
gage - I used one of those a few years ago when I serviced the A/C on
my wife's car. A poorly positioned clip chaffed thru a tube on the
condensor. I found that the pump effectiveness was very dependant on
ambient (or engine compartment temp). If I ran the engine to temp and
then used the venturi vac pump, I could hear as moisture droplets were
pulled out (I had replaced the filter along with the condensor). I
never felt confident that I pulled adequate vacuum (never saw 29 in of
Hg on the gage), but after 2 seasons, the A/C is still functioning
well in her Saturn.

So what is considered an inexpensive micron / thermistor vacuum gage?
After a quick search most of these gages run between $200 to $450.
These would appear to be gages for daily professional use. I found
one gage for $137
http://www.testersandtools.com/Robin...51214350087963.
I expect to use this equipment once every 2 to 3 years.

Are there lower cost gages out there? I am a bit leary of a used gage
- concered about a used gage calibration / function. Would a
dedicated vacuum gage such as this: http://www.valuetesters.com/Yellow-J...cuum-Gauge.php
be better than relying on the manifold gage? If so, I would need to
plumb it into the R134 manifold or connect it to my old R12/R22
manifold gage set and connect that to the other port on the A/C system
during drawn down. With all the money that I will be spending on A/C
parts, I do not have a lot of money left over for additional tools.

FWIW, my '91 F150 has suffered "black death". This Saturday I am going
to play around with flushing the Condenser and Evap (presuming that I
can get the broken off orifice tube out of the evaporator - was using
an orifice removal tool and the end broke off anyway) but
realistically I anticipate replacing condensor, evaporator and suction/
pressure hose (with integral muffler) along with the accumultor and
compressor; so I would be pulling a vacuum on virtually a new A/C
circuit.